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Where Computer Science begins

Updated: Mar 22


0

1

zero

one


That's where Computer Science begins. At zero and one. At data.


There's an input data, and an electric computer gives you a computed output data. Input and output. A computer counts(computes) zeros and ones. It does this with the (1) binary number system, (2) logic gates with transistors, and (3) electronics (electricity and circuits). With these three things we can build a computer, from basic to the most complex.


Computer science is the study of processes that interact with data and that can be represented as data in the form of programs. It enables the use of algorithms to manipulate, store, and communicate digital information. A computer scientist studies the theory of computation and the design of software systems.


A single bit or 1 bit of data is the smallest form of data that the computer reads


BINARY NUMBER SYSTEM


The binary number system only uses two digits from the decimal system, 1 and 0. Hence the name a digital computer.


These two numbers are called states. 1 is on, 0 is off. On meaning an electric current with voltages passes, 0 meaning no electric current passes.


The other decimal numbers like 2,3,4,5,6,7,8,9,10,11 etc are represented only with 1s and 0s using the binary system to count.


We count for example the number 256 in decimal as adding

2x100 =200

5x10 = 50

6x1 =6

SUM 256


Decimal means deci, meaning 10 in latin. Decimal system has only 10 symbols, 0-9, for each digit.


Each base is increasing by a factor of 10 (1, 10, 100) and then multiplied by a number from 0-9 (2, 5, 6, in this case). This system is called base 10. base 10 or decimal system.


Base 10 = Base 2


0 = 0


1 = 1


2 = 10


3 = 11


4 = 100


5 = 101


6 = 110


7 = 111


8 = 1000


9 = 1001


10 = 1011


Here are some larger values:


Decimal: 20 25 30 40 50 100 200 500

Binary: 10100 11001 11110 101000 110010 1100100 1100100 0111110100


A single binary digit (like "0" or "1") is called a "bit".

For example 11010 is five bits long.

The word bit is made up from the words "binary digit" The largest number a digital computer can hold is:


Unsigned - i.e. representation without negative numbers - it will be 2^64–1

18,446,744,073,709,551,615


However, if the representation needed includes negative numbers, the leading bit is used as a sign bit. The range is -2^63 to (2^63)-1.

i.e.

-9,223,372,036,854,775,808 to 9,223,372,036,854,775,807


Addition in Base 10:


A + B = Sum

1 + 2 = 3

If the result is > 9 we 'carry over'

9+1= 0 carry 1 (10)


Addition in Base 2:


A + B = Sum

1+0=1

if result is >1 we carry over

1+1=0 carry 1(10)


4 possible results:

A B Sum

0 + 0 = 0

1 + 0 = 1

0 + 1 = 1

1 + 1 = 1 carry 1


If binary is a system of counting, what do they mean when they say spell in binary?


They mean how to spell things with ASCII

American

Standard

Code

Information

Interchange


a way to convert computer language, or machine code, 1 and 0, into letters. It assigns a characters by a byte of binary.


8 BITS are 1 BYTE


8 digits of binary can represent up to 255 possible values, ASCII has 255 letters, numbers, punctuation marks, and symbols.


UNICODE was created as a standard to take care of other symbols in Japanese, Russian, Greek, Chinese, etc.


A kilobyte (KB) is 1,024 bytes. A megabyte (MB) is 1,024 kilobytes. A gigabyte (GB) is 1,024 megabytes. A terabyte (TB) is 1,024 gigabytes.


In order to represent the logic required to get the possible range of inputs to the desired output we used in these earlier operations, we used logic, or as they are more commonly called in electronics, logic gates.


LOGIC GATES - GATING & LOGIC UNITS


Boolean logic can only have two inputs, true or false (1 or 0), and two outputs, true or false (1 or 0).


Basic BOOLEAN math operations for logic gates to count in binary.


AND - if (A =1 and B =1) THEN OUT = 1, if (A =0 and B =0) THEN OUT = 0

OR - if (A =1 or B =1) THEN OUT = 1

NOT - if (A =1) THEN OUT = 0


In total, there are seven logic gates: AND, OR, XOR, NOT, NAND, NOR, and XNOR.


You can make any of the seven logic gate by combining any of the basic three.


How many logic gates are in a CPU? Logic circuits include such devices as multiplexers, registers, arithmetic logic units (ALUs), and computer memory, all the way up through complete microprocessors, which may contain more than 100 million gates.

The processor uses gates in combination to perform arithmetic functions; it can also use them to trigger the storage of data in memory. Logic gates operate via hardware known as a switch – in particular, a digital switch, called a transistor.


We need to understand the basics of "digital" transistors (specifically CMOS) with the "Full Adder" -- the minimum completely general purpose circuit capable of addition/subtraction including carry-in and carry-out.


Arithmetic Circuits Definition An arithmetic circuit is a set of gates with a separate set of inputs for each number that has to be processed. The gates are connected so as to carry out an arithmetic action and the outputs of the gate circuit are the digits of the result (addition, subtraction, multiplication, or division).Adder Circuits Definition The rules of binary addition for two bits are


0 + 0 = 0

0 + 1 = 1

1 + 0 = 11 + 1 = 0 and carry 1 (the binary number 10; denary 2).

The simplest possible adder circuit for binary digits is called a half-adder, and it allows two bits to be added, with a main output and a carry bit. The truth table is illustrated in Figure 10.9, and this illustration also indicates that the half-adder can be constructed by using a combination of an exclusive-OR gate and an AND gate. The carry bit is 0 except when both inputs bits are 1, which is as required by the rules of binary arithmetic.


Figure 10.9. (a) A half-adder circuit, with (b) symbol and (c) truth table

This half-adder is such a useful circuit that it is made in IC form in its own right, and it can, in turn, be used to create other circuits. The name ‘half-adder’ arises because it can be used only as a first stage in an adder circuit. If we need to add only two bits, the half-adder is sufficient, but if we need to add, say, eight pairs of bits, as when we add two bytes, then the other adders will have three inputs: the bits that are to be added plus the carry bit from the previous stage. For example, adding 1011 and 0011 can use a half-adder for the lowest order pair, giving a 0 output and a carry bit. The addition of the next bits is 1 + 1 + 1, because of the carry, and this gives a 1 output and a 1 carry. The next addition uses the carry from the previous stage, and the last addition uses no carry: Carry 0110

A 1011

B 0011

Sum 1110 If we have the half-adder in IC form, we can connect two half-adders along with an OR gate to provide a full adder, which allows a carry input as well as a carry output. Figure 10.10 shows the circuit, its truth table, and the block representation.


Figure 10.10. (a) The full adder constructed from gates and (b) its symbol


Note A full adder can be used as a half-adder if the carry input is connected permanently to the 0 voltage level.In practice, adders can be serial or parallel. A serial adder works on each pair of bits (and any carry) at a time, adding the figures much as we do with pencil and paper. The only complication is the need to store the bits, and we shall see how this is done in Chapter 11. A parallel adder will have as many inputs as there are bits to add, and the outputs will appear as soon as the inputs are present. This is very much faster, and though the circuit is more complicated, this is no problem when it can be obtained in IC form. Figure 10.11 shows what is involved in a typical parallel adder circuit for two 4-bit binary numbers. In this circuit, all of the inputs are applied at the same time, and the only delay is due to the carry bits, because the addition at each of the later stages is not complete until the carry bit has been generated at the previous stage. This typically takes a few nanoseconds per stage, and the process of passing the carry bit from stage to stage is called rippling through.


Figure 10.11. A 4-bit parallel adder for two binary numbers

Note Since there is never a carry input at the least significant stage, this could use a half-adder, but when the circuit is constructed in IC form a full adder with the first carry set to zero is normally used.Subtraction Definition

The rules for binary subtraction are:

0 − 0 = 0

0 − 1 = −1 (borrow 1)

1 − 0 = 1

1 − 1 = 0


where the −1 entry represents a borrow (or carry-back) action from the next higher bit, rather than the carry-forward operation that is used for addition. Figure 10.12 shows how a half-subtractor circuit can be constructed using a NOT gate added to the simple half-adder circuit. Once again, the ‘half’ reminds you that this circuit does not provide for a borrow, and a two-bit full subtractor circuit can be made using half-subtractors as shown in Figure 10.13. A single stage like this can be used for serial subtraction.

Figure 10.12. (a) The half-subtractor in gate form and (b) as a symbol As you might expect, a full subtractor can be made in parallel form, and an example which provides for two 4-bit numbers is illustrated in Figure 10.14 using full subtractor units. This, however, can also be built using full adder circuits, using a method of subtraction that we need not worry about at the moment (twos complement with end-around carry). The point is that it allows subtractors to be made using the same IC components as adders, making production more economical.


Multiplication and Division Definition

The rules of binary multiplication are:

0 × 0 = 0

0 × 1 = 0

1 × 0 = 0

1 × 1 = 1


and the rules for division are:

0 ÷ 1 = 0

1 ÷ 1 = 1


There are only two division rules, because division by zero is meaningless.

Multiplication and division cannot be carried out by gates alone, because they must be done stage by stage. Consider, for example, a multiplication carried out in the same way as we would multiply two denary numbers: 1101101000001101.0000..1101...10000010

This starts by multiplying each bit in the upper number by the lowest order bit in the second number, producing in this example a set of zeros. Each bit in the second number (the multiplier) will result in a set of 4 bits (in this example) for the result, and each successive set is shifted left by one place. This action of storage and shifting requires the use of registers (see Chapter 11), and this is followed by an addition, in this case of four 4-bit numbers, to find the final result, which may contain a carry to an extra bit position. Division requires the same types of actions and follows the methods used for long division of denary numbers (once familiar to eight-year-olds, but now a lost art in schools). Just as well we can assemble arithmetic circuits that are ready-made for us.



TRANSISTORS


You can make logic gates with transistors in a electrical circuit. Each transistor is a binary bit.


A transistor is a semiconductor device used to amplify or switch electronic signals and electrical power. It is composed of semiconductor material usually with at least three terminals for connection to an external circuit.


Basically a transistor is a current switch, a switch like the one you have in your room to turn on or off the lights. However, these switches are much more sophisticated.


For example, a NOT gate/Intervter has 2 transistors(pmos and nmos). A two input AND gate has a minimum of 6 transistors. If you are a computer architect then you'd have to deal with some thousands or millions of logic gates which further translates to millions/billions of transistors. AND, OR gates: 3 transistors. NAND, NOR gates: 2 transistors.


Transistors can turn on off states millions of times per second.


A transistor has a structure of three parts: An emitter, a base, and a collector.


Here's how a microscopic transistor looks like in a chip:


The transistor is a key area of the chip and the focal point for increasing its speed. Manufacturers are continually improving their designs, making these devices smaller and more densely packed in each square millimeter of silicon. However, to make these transistors work reliably at the more advanced technology nodes, new materials and designs are needed.


Historical note: The first computer was an abacus, following a base 10 system to count. The second computer was an analytical ... Then came mechanical relays to control flow of electrons one way with a diode, replaced by electro-mechanical vacuum tubes to control two ways the flow of electrons, and finally the transistor to switch on and off a current as a solid state using quantum mechanics.


A vacuum tube, an electron tube, or valve or, colloquially, a tube, is a device that controls electric current flow in a high vacuum between electrodes to which an electric potential difference has been applied.


CIRCUIT LOGIC DESIGN & DIAGRAMS


Here's a mask schematic of an old 4004 CPU. The mask is used in the Photolithography part of making a microcheap explained below.


Here you can see a computer design of a chip with billions of transistors:


Mapping processor to circuit diagram:



The diagram maps to a circuit diagram like this:


Roughly a computer is organized (in terms of fields of study) like this from highest level of abstraction to the most physical reality:


Application Software

Virtual Machine

Operating System

BIOS

Embedded Systems

IP Blocks (Sub-units/Peripherals)

Logical Blocks

Gate-Level

Transistor Level

Semicoductors

Device Physics


Computer engineering Topics:

Boolean algebra

logic gates

logic circuit simplification

combinational logic modules

number systems and arithmetic modules

registers

counters

state machines

memory

datapaths

assembly language



INTEGRATED CIRCUIT PROCESSOR


A circuit is a closed loop that electrons can travel in. A source of electricity, such as a battery, provides electrical energy in the circuit. Unless the circuit is complete, that is, making a full circle back to the electrical source, no electrons will move.


An integrated circuit, or IC, is small semiconductor chip that can function as the microprocessor, or computer memory chip. An IC is a small wafer, usually made of silicon, that can hold anywhere from hundreds to millions of transistors.


A computer semiconductor chip groups together billions of transistors in an integrated circuit.


An Intel chip: The 9th gen dubbed Coffee Lake Refresh brought an 8-core i7 variant (eg: i7-9900K) with a die size of 174 mm² which yields just under 3 Billion transistors. On the HEDT side, an 18-core Skylake-X chip clocks in at 485 mm² for around 8.33 Billion transistors.


Interconnects, the conductive metal wires that connect transistors and other elements of an integrated circuit, are critical to the speed and reliability of a microchip. Because modern microprocessors can have as many as ten levels of interconnects, this intricate structure is one of the most process-intensive – thus most costly – portions of the total chip fabrication process.


HOW A COMPUTER CHIP IS CREATED - FROM SAND TO CPU


Start with sand

The process of creating a computer chip begins with a type of sand called silica sand, which is comprised of silicon dioxide.

Silicon is the base material for semiconductor manufacturing and must be pure before it can be used in the manufacturing process.


Silicon ingot

Multiple purification and filtering processes are performed in order to deliver electronic-grade silicon, which has a purity of 99.9999%.

A purified silicon ingot, which weighs around 100kg, is shaped from melted silica and made ready for the next step.


Cut wafers

The circular silicon ingot is sliced into wafers as thin as possible while maintaining the material’s ability to be used in the fabrication process.

The silicon wafers are then refined and polished in order to provide the best possible surface for the following fabrication steps.


Photolithography

After being polished and readied for the process, a layer of photoresist is spread thinly across the wafer.

This layer is then exposed to a UV light mask, which is shaped in the pattern of the microprocessor’s circuits.

Exposed photoresist becomes soluble and is washed off by a solvent.


To pack billions of transistors on today’s most advanced microchips, manufacturers must seemingly defy the laws of physics, using complex lithography methods to print, or “pattern” the wafer with chip features that can be a thousand times smaller than a human hair.


Photomasks support the remarkable progress in transistor scaling by enabling chip designs with billions of devices. Increasing transistor complexity, combined with the extension of 193nm optical lithography, will require 80 or more photomasks per chip design at the 7nm node.


Ions and Doping

Exposed photoresist is washed off and the silicon wafer is bombarded with ions in order to alter its conductive properties – this is called doping.

The remaining photoresist is then washed off, revealing a pattern of affected and unaffected material.


Etching

A pattern of hard material is applied to the wafer using another photolithography step.

Chemicals are then used to remove unwanted silicon, leaving behind thin silicon ridges.

After this, more photolithography steps are applied – which create more of the transistor structure, depending on which gate formation is being used.


Electroplating

An insulation layer is applied to the surface of the almost-complete transistor and three holes are etched into it.

Next, manufacturers use a process called electroplating to deposit copper ions on the surface of the transistor, forming a layer of copper on top of the insulation.

The excess copper is polished off, leaving only three copper deposits in the insulation layer holes.


Layering Interconnects

All the transistors are now connected in an architecture which allows the chip to function like a processor.

The layering and design of these interconnects is incredibly complex, and there can be over 30 layers of metal connections in a single processor.


Test and Slice Die

The chips on the wafer are now ready to be tested.

The wafer is sliced into dies, and functional dies move on to the final step in the fabrication process.


Packaging

Dies are packaged with a substrate and heat spreader, and assume the familiar form factor of a desktop processor.

The heat spreader conducts heat away from the silicon and into the heatsink mounted on top of it.

Processors are then tested for power efficiency, maximum frequency, and other performance metrics.

Those that pass are then packaged as a retail product.







The Ruby-Cutting Procedure A few words about composite drawing and ruby cutting are in order, since the terms may sound foreign to today’s chip designers, who do everything sitting in front of a workstation screen. The chip composite layout was drawn by hand with a straightedge and colored lead pencils at 400 to 500 times the actual scale, in a large, reclining drafting table over a Mylar quadrille sheet— Mylar was used for dimensional stability. The composite layout included all the masking layers of the chip superimposed with their proper registration. Since the composite could not be used directly to generate the masks necessary for the manufacturing process, it was necessary to prepare a separate layer for each mask, to be photoreduced into a “reticle,” a ten-times-larger version of one of the masks for the chip. The artwork used for generating a reticle was called rubylith, or ruby for short, and was obtained by first laying a sheet of Mylar covered by a thin red film over the composite drawing—which served as a guide—on a precision cutting table. The red film on the Mylar was cut and peeled off with tweezers in correspondence with the areas to be etched on the chip, thus producing a rubylith of the same size as the composite drawing, but showing only one of its layers. The large ruby would then be photographed in a gigantic camera and reduced to a blackand-white reticle at ten times magnification. The reticle would then be mounted on a special “step-and-repeat” camera, which reduced the image to actual size and repeatedly exposed it onto a photographic glass plate until the plate’s entire surface was covered with an array of patterns. This process produced the “master,” out of which “submasters” and then “working plates” would be produced by contact photography. The working plates were then mounted in the lithographic equipment that transferred the pattern to the silicon wafers.


A mask:


Whole visual process of making a chip:





Types of Microchips


It is important to differentiate between the main types of microchips, since the leading manufacturers for each are different. We generally classify microchips into DRAM memory, NAND/NOR flash memory, or microprocessors.


DRAM, or Dynamic Random Access Memory, is common memory used in personal computers, desktops, laptops, workstations, and video games platforms.


NAND Flash and NOR Flash are types of flash memory. NAND is used as main memory, in memory cards, solid state drives, and USB flash drives for storage and data transfer. NOR is used mainly as reliable code storage (boot, application, OS, and execute-in-place code) and has some data storage capability.


Microprocessors are often used in personal computers for communication via the Internet, computation, multimedia display, and text editing. Other microprocessors are used in appliances, automobiles, cell phones, and industrial processes.


Computer science is an umbrella term which encompasses four major areas of computing: theory, algorithms, programming, languages. In grad school, you specialize in what kind of computing.


electrical engineering looks at the physical circuit properties, while computer science looks at the practical application of moving bits.


Electrical engineering is an engineering discipline concerned with the study, design and application of equipment, devices and systems which use electricity, electronics, and electromagnetism.


The smallest transistor ever produced (so far) are just 5 nanometers wide(one atom thick, and 10 wide). They were made from graphene, which is being studied to replace silicon.


ELECTRONICS


Electronics comprises the physics, engineering, technology and applications that deal with the emission, flow and control of electrons in vacuum and matter. This distinguishes it from classical electrical engineering as it uses active devices to control electron flow by amplification and rectification rather than just using passive effects such as resistance, capacitance and inductance. The identification of the electron in 1897, along with the subsequent invention of the vacuum tube which could amplify and rectify small electrical signals, inaugurated the field of electronics and the electron age. This distinction started around 1906 with the invention by Lee De Forest of the triode, which made electrical amplification of weak radio signals and audio signals possible with a non-mechanical device. Until 1950, this field was called "radio technology" because its principal application was the design and theory of radio transmitters, receivers, and vacuum tubes.


The term "solid-state electronics" emerged after the first working transistor was invented by William Shockley, Walter Houser Brattain and John Bardeen at Bell Labs in 1947. The MOSFET (MOS transistor) was later invented by Mohamed Atalla and Dawon Kahng at Bell Labs in 1959. The MOSFET was the first truly compact transistor that could be miniaturised and mass-produced for a wide range of uses, revolutionizing the electronics industry, and playing a central role in the microelectronics revolution and Digital Revolution. The MOSFET has since become the basic element in most modern electronic equipment, and is the most widely used electronic device in the world.


Electronics is widely used in information processing, telecommunication, and signal processing. The ability of electronic devices to act as switches makes digital information-processing possible. Interconnection technologies such as circuit boards, electronics packaging technology, and other varied forms of communication infrastructure complete circuit functionality and transform the mixed electronic components into a regular working system, called an electronic system; examples are computers or control systems. An electronic system may be a component of another engineered system or a standalone device. As of 2019 most electronic devices use semiconductor components to perform electron control. Commonly, electronic devices contain circuitry consisting of active semiconductors supplemented with passive elements; such a circuit is described as an electronic circuit. Electronics deals with electrical circuits that involve active electrical components such as vacuum tubes, transistors, diodes, integrated circuits, optoelectronics, and sensors, associated passive electrical components, and interconnection technologies. The nonlinear behaviour of active components and their ability to control electron flows makes amplification of weak signals possible.


The study of semiconductor devices and related technology is considered a branch of solid-state physics, whereas the design and construction of electronic circuits to solve practical problems come under electronics engineering. This article focuses on engineering aspects of electronics.


Intel and Applied Materials make microchips, Intel R&D/designing them and Applied Materials manufacturing them.


MAKING A MEMORY CHIP Ever wondered how memory is manufactured? Here’s a behind-the-scenes look at the rigorous process we undertake to manufacture memory and ensure that you get a high-quality product.


Part I: From silicon to finished wafer

Memory chips are integrated circuits with various transistors, resistors, and capacitors that must be formed on each and every chip. These integrated circuits begin as silicon, which is usually extracted from sand. Turning silicon into memory chips is an exacting, meticulous procedure involving engineers, metallurgists, chemists and physicists.Memory is produced in a large facility called a fab, which contains many clean room environments. Semiconductor memory chips are manufactured in clean rooms because the circuitry is so small that even tiny bits of dust can damage it. Micron's main facility in Boise covers over 1.8 million square feet and has class 1 and class 10 clean rooms. In a class 1 clean room, there is no more than 1 particle of dust in a cubic foot of air. In comparison, a clean, modern hospital has about 10,000 dust particles per cubic foot of air. The air inside a clean room is filtered and circulated continuously. Production team members wear special caps, gowns, and masks that help keep the air particle-free.


Step 1: Silicon ingots The first step from silicon to integrated circuit is the creation of a pure, single-crystal cylinder, or ingot, that is made of silicon and that measures six to eight inches in diameter. Once formed, silicon ingots are sliced into thin, highly polished wafers that are either six or twelve inches in diameter and less than 0.025 inches thick. The circuit elements of the chip (transistors, resistors, and capacitors) are then constructed in layers on the silicon wafer. Circuits are developed, tested by simulation, and perfected on computer systems before they are actually built. When the design is complete, glass photomasks are made—one mask for each layer of the circuit. Photomasks are opaque plates with holes or transparencies that allow light to shine through in a defined pattern, and these masks are essential to the next step in the manufacturing process: photolithography.


Step 2: Photolithography In the sterile clean room environment, wafers are exposed to a multi-step photolithography process which is repeated once for each mask required by the circuit. Masks are used (a) to define the different parts of a transistor, capacitor, resistor, or connector that will complete the integrated circuit, and (b) to define the circuitry pattern for each layer on which the device is fabricated.At the beginning of the production process, bare silicon wafers are covered with a thin layer of glass, followed by a nitride layer. The glass layer is formed by exposing the silicon wafer to oxygen at temperatures of 900 degrees Celsius for an hour or more, depending on how thick the layer needs to be. Glass (silicon dioxide) is formed when the silicon material in the wafer is exposed to oxygen. At high temperatures, this chemical reaction (called oxidation) occurs at a very fast rate.


Step 3: Photoresist Next, the wafer is uniformly coated with a thick, light-sensitive liquid called photoresist. Portions of the wafer are selected for exposure by carefully aligning a mask between an ultraviolet light source and the wafer. In the transparent areas of the mask, light passes through and exposes the photoresist.When exposed to ultraviolet light, photoresist undergoes a chemical change, which allows a developer solution to remove exposed photoresist and leave an unexposed portion on the wafer. For each mask required by the circuit, the photolithography/photoresist process is repeated.


Step 4: Etch In the etch step, wet acid or plasma dry gas is placed on the wafer to remove the portion of nitride layer that is unprotected by hardened photoresist. This leaves a nitride pattern on the wafer in the exact design of the mask. When the hardened photoresist is removed (cleaned) with another chemical, hundreds of memory chips can now be etched onto the wafer.


Part II: Layering the wafer and completing the circuit In Part I of the manufacturing process, all of the circuit elements (transistors, resistors, and capacitors) were constructed during the initial mask operations. The next steps connect these elements together by creating a set of layers.


Step 5: Aluminum layering To begin connecting the circuit elements together, an insulating layer of glass (called BPSG) is deposited on the wafer, and a contact mask is used to define the contact points (or windows) of each of the circuit elements. After contact windows are etched, the entire wafer is covered with a thin layer of aluminum in a sputtering chamber. When a metal mask is applied to the aluminum layer, a network of thin metal connections or wires is formed, creating a path for the circuit.


Step 6: Passivation layering The entire wafer is then covered with an insulating layer of glass and silicon nitride to protect it from contamination during assembly. This protective coating is called the passivation layer. A final mask and passivation etch process follows, removing the passivation material from terminals, which are called bonding pads. The now-free bonding pads are used to electrically connect the die to metal pins on the plastic or ceramic package, and the integrated circuit is now complete.Before the wafer is sent to die assembly, every integrated circuit on the wafer is tested. Functional and nonfunctional chips are identified and mapped into a computer data file. A diamond saw then cuts the wafer into individual chips. Nonfunctional chips are discarded and the rest are ready to be assembled. These individual chips are referred to as die.Before die are encapsulated, they are mounted to lead frames where thin gold wires connect the bonding pads on the chip to the frames to create an electrical path between the die and lead fingers.


Part III: Die preparation and testing In Part II of the manufacturing process, the integrated circuit was created and the finished wafer was cut into dies. The next steps prepare the die for use in finished modules.


Step 7: Encapsulation During Encapsulation, lead frames are placed onto mold plates and heated. Molten plastic material is pressed around each die to form its individual package. The mold is opened, and the lead frames are pressed out and cleaned.


Step 8: Electroplating Electroplating is the next process where the encapsulated lead frames are "charged" while submerged in a solution of tin and lead. Here, the tin and lead ions are attracted to the electrically charged lead frame, which creates a plated uniform deposit, increasing the conductivity of the die and providing a clean surface so that the die can be mounted.


Step 9: Trim and form In trim and form, lead frames are loaded into trim-and-form machines, where leads are formed and the chips are then severed from the frames. Individual chips are then put into antistatic tubes for handling and transportation to the test area for final testing.


Step 10: Burn-in testing In burn-in testing, every chip is tested to see how it performs under accelerated stress conditions. Burn-in testing is a critical component of module reliability. By testing modules in accelerated stress conditions, we’re able to weed out the few modules in every batch that will fail after minimal use. To conduct burn-in testing, we use industry-leading AMBYX ovens that our engineers developed specifically for burn-in testing. Once memory chips pass burn-in testing, they are inspected, sealed, and ready to be assembled.


Step 11: PCB assembly and construction Once memory chips are made, they need a way to be connected to your computer’s motherboard. Printed circuit board (PCB) solves this problem by providing a to connect the chips to your system’s motherboard. To accomplish this, chips are mounted to printed circuit board (PCB) and the final product is a finished memory module.PCBs are built in arrays, or sheets, which are made up of several identical boards. After assembly, the array gets separated into individual modules, similar to how a chocolate bar can be broken into smaller squares. By varying the total number of PCBs in each array based on size, Micron maximizes the number of modules made from a given amount of raw materials.Part IV: Module assembly In Part III of the manufacturing process, the die and PCB were prepared for final module assembly. The final steps cover the module assembly process.


Step 12: Screen print When the module design is perfected and the PCBs produced, memory module assembly begins! Assembly entails an intricate soldering procedure that attaches memory chips to the PCB. This begins with screen printing.In screen printing, a stencil is used to screen solder paste onto finished PCB. Solder paste is a tacky substance that holds chips in place on the PCB. The use of the stencil ensures that solder paste affixes only where components (chips) will attach. The points of attachment are easy to find, thanks to fiducials, which are marks on the PCB that determine where chips need to be placed.Once the solder paste has been applied, automated “pick and place” assembly machines scan the fiducials to determine where to place chips on the PCB. Pick and Place machines are programmed to know which chips are placed where, so when a machine picks a chip from a feeder and places it on the PCB, it knows exactly where the chip is at. The chip placement process occurs for all remaining chips and for any other components on the module. Of all the steps in memory manufacturing, this is the fastest: chips are placed on finished PCB in just a few seconds!


Step 13: Soldering and attachment Next, the assembled chips and boards pass through an oven. The heat melts the solder paste into a liquid. When the solder cools, it solidifies, leaving a permanent bond between the memory chips and the PCB. The surface tension of the molten solder prevents the chips from misaligning during this process.Once the chips are attached, the array is separated into individual modules. Micron team members visually inspect each module. Many modules also undergo additional inspections using automated X-Ray equipment to ensure that all joints have been soldered properly. All Micron Memory Modules meet IPC-A-610 acceptance criteria - the industry standard recognized worldwide.


Step 14: Post-assembly Quality Testing Micron then tests and tags the modules. We use custom equipment to automatically test performance and functionality. This eliminates any possibility of an operator mistakenly placing a failed module in a passing location. Certain modules are programmed with an identifying "Dog Tag" that your PC will recognize and read.


Step 15: Shipment Before being sent out to computer manufacturers and consumers, a statistically significant portion of finished modules are randomly selected for a final quality inspection. Once modules are approved for use, they are placed into ESD-safe plastic trays and bags, and are made ready for delivery. After an extensive manufacturing process, your memory is ready for use. It’s been rigorously tested and approved!


SEMICONDUCTOR MEMORY


Semiconductor memory is a digital electronic semiconductor device used for digital data storage, such as computer memory. It typically refers to MOS memory, where data is stored within metal–oxide–semiconductor (MOS) memory cells on a silicon integrated circuit memory chip.[1][2][3] There are numerous different types using different semiconductor technologies. The two main types of random-access memory (RAM) are static RAM (SRAM), which uses several transistors per memory cell, and dynamic RAM (DRAM), which uses a single transistor and MOS capacitor per cell. Non-volatile memory (such as EPROM, EEPROM and flash memory) uses floating-gate memory cells, which consist of a single transistor per cell.


Most types of semiconductor memory have the property of random access,[4] which means that it takes the same amount of time to access any memory location, so data can be efficiently accessed in any random order.[5] This contrasts with data storage media such as hard disks and CDs which read and write data consecutively and therefore the data can only be accessed in the same sequence it was written. Semiconductor memory also has much faster access times than other types of data storage; a byte of data can be written to or read from semiconductor memory within a few nanoseconds, while access time for rotating storage such as hard disks is in the range of milliseconds. For these reasons it is used for main computer memory (primary storage), to hold data the computer is currently working on, among other uses.


MEMORY CELL


The memory cell is the fundamental building block of computer memory. The memory cell is an electronic circuit that stores one bit of binary information and it must be set to store a logic 1 (high voltage level) and reset to store a logic 0 (low voltage level). Its value is maintained/stored until it is changed by the set/reset process. The value in the memory cell can be accessed by reading it.


Over the history of computing, different memory cell architectures have been used, including core memory and bubble memory. Today, the most common memory cell architecture is MOS memory, which consists of metal–oxide–semiconductor (MOS) memory cells. Modern random-access memory (RAM) uses MOS field-effect transistors (MOSFETs) as flip-flops, along with MOS capacitors for certain types of RAM.

The SRAM (static RAM) memory cell is a type of flip-flop circuit, typically implemented using MOSFETs. These require very low power to keep the stored value when not being accessed. A second type, DRAM (dynamic RAM), is based around MOS capacitors. Charging and discharging a capacitor can store a '1' or a '0' in the cell. However, the charge in this capacitor will slowly leak away, and must be refreshed periodically. Because of this refresh process, DRAM uses more power, but can achieve greater storage densities.


On the other hand, most non-volatile memory (NVM) are based on floating-gate memory cell architecture. Non-volatile memory technologies including EPROM, EEPROM and flash memory use floating-gate memory cells, which are based around floating-gate MOSFET transistors.


DRAM MEMORY CELL


Storage

The storage element of the DRAM memory cell is the capacitor labeled (4) in the diagram above. The charge stored in the capacitor degrades over time, so its value must be refreshed (read and rewritten) periodically. The nMOS transistor (3) acts as a gate to allow reading or writing when open or storing when closed.


Reading

For reading the Word line (2) drives a logic 1 (voltage high) into the gate of the nMOS transistor (3) which makes it conductive and the charge stored at the capacitor (4) is then transferred to the bit line (1). The bit line will have a parasitic capacitance (5) that will drain part of the charge and slow the reading process. The capacitance of the bit line will determine the needed size of the storage capacitor (4). It is a trade-off. If the storage capacitor is too small, the voltage of the bit line would take too much time to raise or not even rise above the threshold needed by the amplifiers at the end of the bit line. Since the reading process degrades the charge in the storage capacitor (4) its value is rewritten after each read.


Writing

The writing process is the easiest, the desired value logic 1 (high voltage) or logic 0 (low voltage) is driven into the bit line. The word line activates the nMOS transistor (3) connecting it to the storage capacitor (4). The only issue is to keep it open enough time to ensure that the capacitor is fully charged or discharged before turning off the nMOS transistor (3)


MOSFET


The metal–oxide–semiconductor field-effect transistor (MOSFET, MOS-FET, or MOS FET), also known as the metal–oxide–silicon transistor (MOS transistor, or MOS), is a type of insulated-gate field-effect transistor (IGFET) that is fabricated by the controlled oxidation of a semiconductor, typically silicon. The voltage of the covered gate determines the electrical conductivity of the device; this ability to change conductivity with the amount of applied voltage can be used for amplifying or switching electronic signals. The MOSFET was invented by Egyptian engineer Mohamed M. Atalla and Korean engineer Dawon Kahng at Bell Labs in November 1959. It is the basic building block of modern electronics, and the most frequently manufactured device in history, with an estimated total of 13 sextillion (1.3 × 1022) MOSFETs manufactured between 1960 and 2018.

The MOSFET is the most common semiconductor device in digital and analog circuits, and the most common power device. It was the first truly compact transistor that could be miniaturised and mass-produced for a wide range of applications, revolutionizing the electronics industry and the world economy, having been central to the computer revolution, digital revolution, information revolution, silicon age and information age. MOSFET scaling and miniaturization has been driving the rapid exponential growth of electronic semiconductor technology since the 1960s, and enables high-density integrated circuits (ICs) such as memory chips and microprocessors. The MOSFET is considered to be possibly the most important invention in electronics, as the "workhorse" of the electronics industry and the "base technology" of the late 20th to early 21st centuries, having revolutionized modern culture, economy, society and daily life.


A key advantage of a MOSFET is that it requires almost no input current to control the load current, when compared with bipolar junction transistors (BJTs). In an enhancement mode MOSFET, voltage applied to the gate terminal can increase the conductivity from the "normally off" state. In a depletion mode MOSFET, voltage applied at the gate can reduce the conductivity from the "normally on" state.[2] MOSFETs are also capable of high scalability, with increasing miniaturization, and can be easily scaled down to smaller dimensions. They also have faster switching speed (ideal for digital signals), much smaller size, consume significantly less power, and allow much higher density (ideal for large-scale integration), compared to BJTs. MOSFETs are also cheaper and have relatively simple processing steps, resulting in high manufacturing yield.


MOSFETs can either be manufactured as part of MOS integrated circuit (MOS IC) chips, or as discrete MOSFET devices (such as a power MOSFET). Since MOSFETs can be made with either p-type or n-type semiconductors (PMOS or NMOS logic, respectively), complementary pairs of MOSFETs can be used to make switching circuits with very low power consumption, in the form of complementary MOS (CMOS) logic. The name "metal–oxide–semiconductor" (MOS) typically refers to a metal gate, oxide insulation, and semiconductor (typically silicon).[1] However, the "metal" in the name MOSFET is sometimes a misnomer, because the gate material can also be a layer of polysilicon (polycrystalline silicon). Along with oxide, different dielectric materials can also be used with the aim of obtaining strong channels with smaller applied voltages. The MOS capacitor is also part of the MOSFET structure.

©2020 by Arturo Devesa.