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# Depletion Capacitance

21 Threads found on edaboard.com: Depletion Capacitance

## calculating overall Cgs of MOSFET

Cgs changes with gate potential (see C-V curves). Your channel capacitance under the gate only gets "hooked up" once the channel inverts. Before this it has a varying series depletion capacitance ("off" transitioning to a very-resistive oxide capacitance, to a well connected one. Besides this you have the fringing and (...)

## Is the device capacitance bias-dependent or independent?

Anything with a depletion region on either side of it will be voltage dependent. MOS channels swing from accumulation through depletion to inversion. Cgs follows gate voltage directly; Cgd, only when the channel is well lit near the drain (linear region - when it goes constant current the capacitance is sort of stood off from the (...)

## Is there anybody who knows the equation for calculating Cds for a transistor?

This is going to depend on a lot of things. For the power MOSFET, you're really talking Cdb as the dominant term because B=S by close-in strapping. Then it's raw junction depletion capacitance with Vds dependence (when off) or a pretty good D-S short and not much use in figuring C, when on. Short channel FDSOI MOSFETs, it's really the metallizatio

## range of varactor capacitance

MOS varactor can swing between Cox(W,L) and (Cgso+Cgdo+Cgbo) if you can push the silicon depletion that far without gate ox rupture (or on thin enough SOI). It will not act entirely the same as a PIN varactor as you have a compound capacitor (oxide cap in series with junction cap).

## what is the capacitance component of MOSFET?

If by gate capacitance you mean gate-bulk capacitance then the gate capacitance consists of series combination of oxide capacitance and depletion capacitance. We only have gate-bulk capacitance when device is off. In saturation and triode regions this (...)

Acde is a factor in the exponential coefficient used for the calculation of XDC, the DC charge thickness in accumulation and depletion regions, and is used in the Charge-Thickness capacitance Model mainly to calculate the CGB capacitance correctly - cf. the BSIM documents. You may either ignore these warnings

## NMOS based electronic circuits

Holy 1980s, Batman! That's the last time I worked on an NMOS-only circuit - on 2" wafers in a university lab. Why not set the Wayback Machine to like 1972 and do some sweet PMOS-only stuff? If you want to do NMOS only, you'd like to at least have a depletion-mode load device. Or eat the area and dismal capacitance of a high value N+ resistor (I

## poly to poly and poly to diffusion capacitors

Your poly-diffusion cap will be a MOSCAP. It may be the standard FET gate, or it could be field ox. The threshold voltage of the latter can be expected to vary a lot and its density will be low. Below, or near the VT you can expect a series depletion capacitance to develop. Poly depletion in POP caps can be a problem, the silicidation (if (...)

## Depletion Capacitance in a Diode

Can anyone please tell about the typical (practical) values of depletion capacitance in forward and reverse bias, and also of diffusion capacitance in forward bias? Thanks in Advance

## How does poly sheet resistance affect timing of NMOS/PMOS?

There will be some correlation between the poly doping at the gate ox interface, and device VT. You can see poly-depletion effects sometimes if doping is too low or not driven long enough. Drain risetime will respond to gate resistance and Miller (Cgd) capacitance. Something like Vgs/Rg=Cdg*dVds/dt. Digital delay embodies half the output ris

## schottky and p-n junction in varactor diode

varactor diode is P-N junction device operated in reverse bias. schottky diode is basically metal-semiconductor junction which will have low barrier and fast recovery time. under revers bias the depletion region should be sufficient to have wider capacitance range. so P-n juntion i.e semi-semi (not metal-semi) under reverse bias will have wider

## Thickness of dielectric towards capacitance?

What you should have read was, as the depletion layer is formed beneath the gate oxide of the mosfet, the depletion layer (devoid of mobile charges and therefore essentially an insulator) increases the thickness of the effective dielectric (gate oxide plus the depletion zone) and decreases the capacitance. This (...)

## CJS in Bipolar Device Model

What is "Cjs" in a PNP device model? What's this capacitance physically? It's the zero bias collector-substrate depletion capacitance, s. PDF below. Is there any trick one could use to get the PNP device with large Cjs to run faster? Cjs decreases when the collector-to-substrate voltage increases. A

## Periphery of drain/source

The periphery of the drain is 2*(105nm+90nm), but, e.g. when calculating parasitic capacitances, the 90nm side on the side of the channel is not taken into account because there exists the depletion region under the channel and thus there is no sidewall parasitic capacitance on that side.

## How to compute the channel to bulk capacitance

there is only a reversed diode between the bulk and channel. the x should be the depletion range width.

## Drain diffusion capacitance?

it is due to the depletion layer formed between the drain and the body terminal of the MOS....

## Question about MOSCAP and the depletion region

Hi, When the capacitance of a MOS is measured at high frequencies (assuming it is biased), then no inversion layer is generated, as there are no minority carriers (Assume that gate is biased positive and semiconductor is p-type). Then to compensate for the +ve voltage on the gate of the cap., there has to -ve voltage in the semiconductor. Boo

## about the polarity of cpip capacitor

I cannot affirm nothing concernign the possible depletion arising in the poly. Nevertheless you must keep in mind that the bottom plate has much more parasitic capacitance than the top one. You must see if in your design this effect can be tolerated or not.

## Mos gate capacitance-serious doubt -help sought

Hi all, I have a very serious doubt regarding the capacitance(gate channel ) of is about the capacitance of gate when the voltage(vin) is greater than vt . ppl say that the cap is Cox*W*L . but b4 this it is less due to depletion region (for small vin). what i ask is that even after Vt depeltion layer will be beneath th

## depletion capacitance

What happens to the depletion capacitance in a pn junction dide when the reverse bias voltage is increased!!!!!!!!!!!!