I have been reading about CPUs recently and came to know that all logical blocks and memory on CPU can be made out of transistors. So is it the only electronic component on CPU?

Edit (Made after first two answers):

But the making of CPU only talks about projecting transistor diagrams (May be that is the major part). But how are additional components like diodes, capacitors etc. added to CPU?

  • \$\begingroup\$ Your preferred answer is the soonest one, but not the one with the most votes or the most information in it. It might be nice to change it. \$\endgroup\$
    – pjc50
    Commented Feb 26, 2016 at 16:50
  • \$\begingroup\$ Some types of transistors (MOSFETs) are inherently capacitors and diodes. \$\endgroup\$
    – Nick T
    Commented Feb 26, 2016 at 20:18
  • 5
    \$\begingroup\$ If you have a new question, ask a new question and don't edit the original one \$\endgroup\$
    – PlasmaHH
    Commented Feb 27, 2016 at 9:57
  • \$\begingroup\$ @PlasmaHH By the time I removed the edit and asked a different question, answers started to come for edit also. So I had to keep it there. \$\endgroup\$ Commented Feb 29, 2016 at 4:16
  • \$\begingroup\$ CPUs are not made of components, they are made of patterns of metal and silicon. \$\endgroup\$ Commented Feb 29, 2016 at 4:31

7 Answers 7


The logical blocks and memories can be made out of only transistors. The important question is: are all of the circuits on CPUs logical blocks and memories, or is there anything else?

The answer is, there are always some other circuits. Here are some examples:

  • ESD protection circuits often uses diodes and resistors
  • Internal bypass capacitors: actually these can be made just from transistor gates, but they are often also made in the metal layers.
  • Analog blocks like internal LDO regulators, bandgap references, power-on-reset comparators, etc. are usually best implemented with some resistors among the transistors. It may be possible to get rid of the resistors and use 100% transistors in some of these cases, but it's not necessarily optimal.
  • Internal oscillators may use inductor-capacitor (LC) tank circuits (though inductors are so large that they are not cost-effective on modern general purpose CPUs).
  • Etc., etc.
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    \$\begingroup\$ How often is a "resistor" anything other than a transistor with a really long channel that's biased into the resistive region? And how often do oscillators use LC tank circuits rather than relying upon "parasitic" [though engineered to be large] capacitance within a ring containing an odd number of inverters? \$\endgroup\$
    – supercat
    Commented Feb 26, 2016 at 16:34
  • 4
    \$\begingroup\$ @supercat - for the mixed-signal ICs I work on, there are plenty of real resistors and capacitors. The LC tank circuits I've seen have all been used when the phase noise of a ring oscillator is inadequate. Of course, a mixed-signal IC will have more such circuits than a CPU (or in other words, "I don't know"). \$\endgroup\$
    – Justin
    Commented Feb 26, 2016 at 20:23
  • 2
    \$\begingroup\$ Interestingly, POWER7 used capacitors for embedded DRAM and to avoid voltage drop. \$\endgroup\$
    – user15426
    Commented Feb 27, 2016 at 1:05
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    \$\begingroup\$ This answer is nice enough but I think you can expand it a bit. For the resistor part you imply that resistors can be made with properly biased mosfets, but it is not much clear. \$\endgroup\$ Commented Feb 27, 2016 at 11:56
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    \$\begingroup\$ @VladimirCravero - I wasn't planning to expand my answer to talk about how the components are made. Anyway, a typical resistor I was thinking of would be a long, thin strip of polysilicon. You can use a properly biased mosfet in most cases, but sometimes a resistor is better. \$\endgroup\$
    – Justin
    Commented Feb 27, 2016 at 12:08

I think you have to look at it the other way around: CPUs are made with steps (implantation, lithography, etching, deposition of materials). If you design the steps and layers a certain way you get a CMOS couple (N-type MOSFET on the left, P-type MOSFET on the right), useful for making inverters and then start the whole logic thing, to eventually build all the CPU logic blocks.

enter image description here

But CPUs need other kinds of devices, for ESD or integration of memory or whatever. For that, you can design the layers in another way and get resistors (using the polysilicon layers or the doped substrate), by making a long line thing of material:

enter image description here

This is the crux of what made planar IC technology such a disruptive idea: From simple steps you can build (almost) anything.


The majority of components on a CPU are transistors but other components can be made.

A diode is made from either a PN junction or a metal semiconductor junction with a suitable level of doping in the semiconductor.

A resistor can be made out of a long strip of material (possiblly metal on one of te metal layers, possiblly semiconductor on a semiconductor layer).

A capacitor can be made up of two conductive materials with a thin insulating layer in between (similar to the gate of a mosfet but larger).

The issue with resistors and capacitors is there is no good way to make large values in an IC. Often a resistor or capacitor can end up taking up the same area as many many transistors. It's often cheaper in terms of silicon area to use a special transistor instead of a resistor.


No, there are also diodes, resistors, capacitors and inductors and maybe others too.

  • \$\begingroup\$ But making of CPU only talks about projecting transistor diagrams. Can you give any more information how these components are added to CPU? \$\endgroup\$ Commented Feb 26, 2016 at 14:59
  • \$\begingroup\$ Maybe because transistors form the majority of the circuit. I am not a specialist on IC fabrication, so the exact how to I cannot answer. \$\endgroup\$
    – Bart
    Commented Feb 26, 2016 at 15:02
  • \$\begingroup\$ The question owner accepted this as the best answer. \$\endgroup\$ Commented Feb 26, 2016 at 19:07
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    \$\begingroup\$ The person who asked a question might be in the best position to judge which answer is most applicable to their personal interest, but they are often not in the best position to judge which is most correct or informative. \$\endgroup\$ Commented Feb 26, 2016 at 20:04
  • \$\begingroup\$ What's missing here is that the other components can be incidental or parasitic. Or they can be formed by intentionally manipulating such properties of transistors or degenerate transistors, or from more unique structures. Of course bipolar junction transistors are themselves uncommon in modern ICs compared to insulated gate FETs. \$\endgroup\$ Commented Feb 26, 2016 at 20:07

But how are additional components like diodes, capacitors etc. added to CPU?

Well you can make any electronic components from only silicon.

Silicon has interesting features. Doped silicon is a semiconductor, which means it can make resistors, because any normal conductor has a resistance. It can even be used as wires, although not very efficient. In practice polysilicon will be used, for example the 8087 chips

... consists of a tiny silicon die, with regions of the silicon doped with impurities to give them the desired semiconductor properties. On top of the silicon, polysilicon (a special type of silicon) formed wires and transistors. Finally, a metal layer on top wired the circuitry together


Putting N-P semiconductors together makes a diode, because that's the structure of diodes. Putting P-N-P or N-P-N together makes transistors. When combining with oxygen it becomes silicon dioxide which doesn't conduct anymore and can be used to make the area around wires and conducting elements.

Capacitors are also very easy to create, just an insulator (silicon dioxide) as dielectric between 2 conducting plates (silicon).

With transistors, resistors and capacitors you can make an opamp which then can be used to simulate an inductor without any coil, with even less area consumed than a real induction coil. Cool, isn't it?

simulated inductor

Above is one of the way to create a simulated inductance. You can find more ways to do that in the below references

Of course if you need more inductance or capacitance you may still have to use a separate external coil or capacitor.


It depends on what you mean by "electronic component" and "CPU". If you restrict that to semiconductor devices and the actual processing unit itself, then yes, a CPU is made of transistors.

If you include IOs, you have some higher-voltage transistors and clamp diodes, plus ESD protection cells (which can use transistors and/or diodes). If you allow passive components, you have wires made out of metal or polysilicon. Of course, diodes can be made from BJTs as well.

Transistors and wires are the only components on many integrated circuits, including many CPU chips.

Some microprocessors have other components on the same chip as the processor. If you include the whole chip, then you might have any number of analog components: diodes for temperature measurement, analog to digital converters, LDO voltage regulators, crystal oscillators, sense amplifiers for memory, and (perhaps most commonly) power-on reset circuits. These use passive components. Resistors are the most common, and come in many different types:

  • Polysilicon - Low resistance, okay tolerance, also used for wires
  • N-well - High resistance, terrible tolerance and tempco
  • Diffusion - Kind mediocre
  • Weird stuff like negative tempco resistors

Capacitors tend to be much larger than resistors. They're made out of metal-oxide-semiconductor stacks, or poly-oxide-poly. You can also use the P-N junction capacitance or the capacitance between parallel wires in a metal layer.

Inductors are typically too big to use in any but the highest-frequency circuits (>1 GHz). They're made from spirals of metal.

There are also extra-special transistors like the kind used in flash memory and DRAM. Those are definitely in a class of their own.


There is no such a component like "ideal transistor" in the real world. A transistor is also a resistor, a capacitor, a couple of diodes, a low voltage Zener diode, etc. All these side effects participate in the work of CPU, even if some of them may be unwanted (parasitic elements).

Hence CPU could not be made from "ideal transistors", but the real world transistors can be substituted for other needed elements. However in some cases this is not optimal as dedicated resistors or capacitors are simpler and perform better.


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