# Capacitors in integrated circuit

1. Mar 16, 2005

### cypress7

hi... i'm very glad if you all can help me solving my problem..i want to know what the uses of capacitors in modern integrated circuit chip..i had searched for it in many books but what i found is the uses of capacitors in usual circuit... so please help me...

thanks

Last edited by a moderator: Jan 11, 2012
2. Mar 16, 2005

### chroot

Staff Emeritus
The uses of capacitors in an integrated circuit are exactly the same as the uses of capacitors in any other circuit.

- Warren

3. Jan 10, 2012

Hai, integrated capacitors use is similar to an ordinary capacitor only.An IC is nothing but a collection of active devices(diodes,Transistors), as well as passive components(Resistors,capacitors,inductors).It is easy to fabricate active devices when compared to passive devices like R,L,C components.We have to use specialized methods to fabricate R,L,C.Other than this integrated capacitor function is similar to the ordinary capacitor.
good luck

4. Jan 10, 2012

### Kholdstare

Usually in digital ICs capacitor is unwanted parasitic, which introduces delay. People tries to optimize the capacitance to match with logic gates current output for minimum delay.

In analog ICs capacitors are user in Colpitt and Hartley oscillators. Also Opamps and some analog amplifiers need some value of capacitance for stability concerns.

Capacitors are also used in Butterworth and chebyshev filters. Also capacitors are used in switched capacitor circuits (filters), which is easier to fabricate than resistors. Often some inverting and non-inverting amplifier uses capacitor as voltage dividers than resistors.

Most importantly some feedback circuitry employs capacitor.

Inductor values are most difficult to control in an IC followed closely by resistors.

Last edited: Jan 10, 2012
5. Jan 11, 2012

### Mike_In_Plano

There are a couple of means of forming capacitors in an IC. Reverse biasing a circuit gives you a capacitor, though it's voltage dependent. A nicer variety is formed using oxide as a dielectric and either metalization or heavily doped silicon as a plate.

Capacitors are the basis upon which DRAM is constructed. By occasionally reading the potentials on a group of capacitors and then writing back to them, each one's state can be maintained as a 1 or 0 indefinitely. Of course, with the pressing need for denser and denser memory, the capacitors in RAM are no longer planer. Now, a special etch process actually drills into the silicon forming vast numbers of wells, which are then plated on the backside forming capacitors.

In analog, capacitors are commonly used in the op-amp circuit to establish what is termed the dominate pole. The dominate pole is a frequency, which is established by an RC, and serves to reduce the gain of an op amp versus it's test frequency. Typically, this frequency will be on the order of 10 Hz, and the open loop gain of the op amp will steadily decrease until it's = 1, at the op amps gain bandwidth.

Capacitors are also used in A/D converters of different sorts. It's remarkably easy to control the relative surface area on a chip, so it's easy to define capacitors as being an exact multiple of one another. This is the basis of the very common successive approximation converter. Capacitors are also used in building blocks such as the integrators in delta sigma A/D converters.

Surprisingly, you can even build the equivalent of resistors by using capacitors with mos switches. Thus dividing networks and filters can be fabricated without the need of resistors. The switching frequency and ratio of the capacitors set the properties of these systems.

There are actually quit a few more applications that inventive chip designers have thought up, but I'm sure this gives you a start.

Best Wishes,

Mike

6. Jan 12, 2012

### Kholdstare

DRAM cap! How could I have forgotten those. :D Those caps are not even made just by growing oxide. Their structures stand over the access MOS for high packing density.