Microprocessors: What are they and how do they work?
- Sebastian Kartadjomena
- Jan 4
- 6 min read
Figure 1
Image of an intel microprocessor unit (Right: Front of the microprocessor) (Left: Back of the microprocessor)
(Image taken from electroSome, 2017)
If you ever choose to crack open your smartphone, tablet, computer or car for whatever reason, you’ll find a circuit and in that circuit, you’re sure to find a microprocessor, the component you see in the image above.
A microprocessor is a single semiconductor chip that integrates the main five functional units of a computer: arithmetic/logical, control, storage, input, and output. (tel, n.d.). So, what does any of that even mean? This article will provide a surface-level overview of the function, design and design process of microprocessors such that the reader can appreciate the complexity and intricacies of this component.
Functions of a Microprocessor
You can think of a microprocessor like a brain, taking inputs from its environment, interpreting them, and generating outputs based on its interpretation of those inputs. As previously stated, a microprocessor consists of an Arithmetical and Logical Unit (ALU), Control Unit and Register Array. An ALU performs all arithmetic and logical operations on inputs received from input devices or memory. Register arrays consist of a series of registers that act as temporary fast access memory locations for processing data. In other words, any data processors access data through the register. Finally, the control unit controls the flow of instructions and data throughout the system (George, 2017).
A microprocessor on its own does nothing and must be connected to an external circuit(s) to be useful. Typically in microcomputers, computers which use microprocessors, the microprocessor is connected to external circuits by use of an integrated circuit, an electric circuit made from a solid block of semiconductor material (Crisp, 1998). It allows for circuits to be constructed in a very small space and, many times, is simply called a, ‘chip.’
Design of a Microprocessor
A microprocessor is typically 12 mm across and is easily damaged by external factors in the environment such as abrasion or moisture (Crisp, 1998). Its perimeter is composed of connecting pins jutting out from its sides which act as electrical connections to the main circuit board. The size, shape, and number of pins on the microprocessor is dependent on the amount of data desired to be sent through the microprocessor. See an example of a microprocessor below in figure 3:
Figure 3
Typical microprocessor
(Taken from ELPROCUS, n.d.)
Microprocessors are intricate in their design though this is not at all clear from observation through the naked eye. It is only through magnification tools such as a scanning electron microscope (SEM) that one may appreciate the complexity of a microprocessor. The difference in the observable detail can be seen when comparing figures 4 and 5 which use a digital single-lens reflex (SLR) camera to take images of the microprocessor with figures 6 and 7 which were taken with a SEM. Note that the SEM images’ being in black and white is simply a result of SEM using grayscale to represent what we understand as depth.
Figure 4
Zoomed in view of a microprocessor using a SLR camera
(Image taken from NISENet, 2014)
Figure 5 & 6
Figure 6: (Right) SEM view of a microprocessor at approximately the same magnification as the maximum magnification of the digital SLR camera
Figure 5: (Left) Approximately the most zoomed in view of a microprocessor possible on a digital SLR camera. (Images taken from NISENet, 2014)
Figure 6: (Right) SEM view of a microprocessor at approximately the same magnification as the maximum magnification of the digital SLR camera. (Images taken from NISENet, 2014)
Figure 7
‘Architecture’ of a microprocessor
(Images taken from NISEnet, 2014)
Figures 8 & 9
Figure 8: (Left) Magnification of the ‘architecture’ of the microprocessor. Figure 9 (Right) A single transistor seen outlined by the purple rectangle with channel width of 1000 nm or 1 micron
(Images taken from NISEnet, 2014)
Figures 8 and 9 show a further magnified view of the microprocessor. Figure 9 especially is quite the marvel to think about: The purple box outlining a slightly whiter part of the microprocessor is a transistor, an on and off switch of sorts that allows an amount of current through it that is dependent on the amount of voltage supplied to it. This transistor’s ‘channel’ where current flows, is only 1 micron or 1000 nm wide! To put into perspective how incredible that is, a single human hair is around 100 microns (PMPA, n.d.) so this transistor is approximately 1/100s the size of a hair! The images above showcase an older microprocessor from the late 90s, having transistors that would seem titanic compared to modern transistors. The smallest transistor ever made at the time of this article’s writing was produced by a collaboration between a team at the University of South Wales (UNSW) in Australia and the University of Wisconsin-Madison in the United States, measuring just 4 nm across (Guinness World Record, n.d.).
Design Process of a Microprocessor
Seeing the intricacy of a microprocessor one begins to wonder how exactly a microprocessor is created. I will provide a simple explanation based on the explanations of Rober Elder from Robert Elder Software Inc. (2021) and Bureau EFY from Electronics for You (2023):
First one must get a rock: the more concentrated it is in silicon dioxide (the stuff sand is made from) the better.
Crush that rock into tiny pieces.
Purify it to 99.9% pure silicon dioxide.
Purify further to 99.9999999% polysilicon metal.
Place the polysilicon ingots into crucible and what then to 1698 K.
Figure 10
Machine used for fabrication of the single crystal
(Image taken from Halbleiter, n.d.)
Take a small seed monocrystal and dip it into the molten silicon, slowly pulling the crystal out as it cools. See Figure 10 for an example of the machine used for the fabrication of single crystals of silicon.
Once one has gotten a monocrystal of pure silicon, cut it into thin slices called silicon wafers. To promote energy flow, one could dope the silicon wafer with Boron, Phosphorus or another dopant (WaferPro, 2022).
Put photoresist, a light-sensitive material, on the wafer, used to create patterned coatings on the surface, 9. useful for making a circuit on the wafer (University Wafer, n.d)
Take a chromium etched photo-lithographic quartz mask with your desired circuit pattern and shine a laser beam through it to project the circuit pattern onto the wafer. This is photolithography and figure 11 & 12 below shows an example of the mask as well as the machine that creates the laser beam:
Figures 11 & 12
Figure 11: (Left) Photomask. Figure 12: (right) Photolithography machine creates laser beam used to project circuit pattern from photomask onto silicon wafer
(Figure 11: Taken from Tekscend Photomask, n.d. Figure 12: Taken from IEEE Spectrum, 2018)
The shadows created by the photomask control where the phot-resist is chemically changed on the surface of the silicon wafer (This is dependent on whether one used positive or negative photoresist).
Develop the photoresist.
Acid etch the exposed parts of the wafer.
Perform countless iterations and repetitions of homo-epitaxy, hetero epitaxy: The growing of a material on a substrate of the same chemical composition or otherwise respectively (Kumar et. al, 2018), diffusion doping, copper interconnect layers, chemical mechanical polishing, photoresist applications, acid etching, and photomask exposing to build up the desired features on the wafer.
Cut silicon wafer into pieces then locate the pads, the circle parts, on the silicon chip, and attach bond wires, wires which can connect to one’s system
Use bond wires or solder balls to provide electrical connection between the pins on the chip package, and the pads on the silicon die.
And voila
Figure 13
A CPU
(Image taken from compware, 2023)
A microprocessor
I hope you learned something from all this, I sure did. I made this article because I recently started with electronics; I made one simple Light-emitting diode (LED) system recently where you turn the LED on and off using the switch on the power supply. When I say recent I mean recent. This new interest made me want to learn all about circuits and so I’ve decided to write an article about microprocessors so that I could understand and, through that understanding, perhaps be less scared of such complicated looking devices. I hope you too are less scared. Bye bye.
References:
Bureau, EFY. (2023). The Brain of Computing: Exploring the Intricate Art of CPU Manufacturing. Electronic For
Compare Hardware (compware). (2023). CPU Benchmark. Vi har lavet en analyse af alle de store siders
benchmark. Compware cpu-benchmark-vi-har-lavet-en-analyse-af-alle-de-store-siders-benchmark
Crisp, J. (1998). Introduction to Microprocessors and Microcontrollers. Elsevier.
Elder, R. (2021). How to make a CPU - A Simple Picture Based Explanation. Robert Elder Software Inc.
George, L. (2017). What is a microprocessor?. electroSome
Guinness World Records. (n.d.). Smallest transistor. Guinness World Records
Halbleiter. (n.d). Wafer Fabrication: Fabrication of the single crystal. Halbleiter
Institute of Electrical and Electronics Engineers (IEEE) Spectrum. (2018). ASML Developing NExt-Gen EUV
Lithography>Productivity gains will continue through the next two or three chip generations, but after that we’ll need something bigger and better. IEEE Spectrum https://spectrum.ieee.org/asml-developing-next-gen-euv-lithography
National Informal STEM Education Network (NISENet). (2014). Zoom Into Microchip. NISENet
Precision Machined Products Association (PMPA). (n.d.). Speaking of “Resolution”. PMPA
Tekscend Photomask. (n.d). Photomasks for Semiconductors. Tekscend Photomask
Tokyo Electron Limited (tel). (n.d). What is a microprocessor?. Tel
University Wafer. (n.d). What is Photoresist?. University Wafer
WaferPro. (2022). What Are Doped Silicon Wafers and What Is Their Purpose In SIlicon Wafer?. WaferPro q
Kumar, D. S., Kumar B. J., Mahesh, H. M. (2018). Synthesis of Inorganic Nanomaterials: Advances and Key
Technologies. Elsevier https://www.sciencedirect.com/science/article/abs/pii/B9780081019757000038
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