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To: FJB who wrote (5130)	3/20/1998 10:36:00 PM
From: Yousef	Read Replies (1) \| Respond to of 6843

Bob, Re: "In simplest terms(for the layperson), what is the relationship between linewidth and FET drive currents? Also, what's the formula for this relationship?" In simplest terms, as Leff (physical gate length) decreases, Idsat (drive current) increase. This is fairly linear such that a 10% reduction in Leff gives a 10% increase in Idsat. In more complicated terms, the formula for Idsat --> Idsat = [(ZuC)(Vgs-Vt)^m]/(2Leff) ... Z = FET width ... u = carrier mobility ... C = Gate capacitance ... Vgs = Voltage Gate-to-Source = Operating suppl voltage typically ... Vt = Threshold voltage ... m = Exponent = 1 to 2 (for long Leff, m=2 ... for short Leff, m=1.2) ... Leff = physical gate length (usually about .08um less than printed L) The term (Vgs-Vt) is termed the "gate overdrive voltage", as technologies have moved from .5um to .35um to .25um the operating voltage has decreased from 3.3V to 2.5V to 1.8V while the Vt (threshold of the devices) has decreased very little (from .7V to .4V). Thus the "gate overdrive" has been reduced for each new generation and thus Idsat is very hard to maintain the same as we move to new generations of devices. The way to compensate for this is to decrease Leff and reduce gate thickness (increase gate capacitance). Hope this helps. Make It So, Yousef

To: FJB who wrote (5130)	3/21/1998 1:18:00 AM
From: Pravin Kamdar	Read Replies (1) \| Respond to of 6843

Bob, In the simplest terms, the channel between the two conducting terminals of a FET device is simply a variable resistor whose value is modulated by the gate voltage. Therefore, for any given gate voltage (and neglecting back bias), the resistance is directly proportional to the distance between the terminals, the gate length. So, if gate length goes down, resistance goes down, and current between the terminals goes up. A model describing the proportionality being given in Yousef's post. A very simple trans-resistance concept, with the device being coined a "transistor". Pravin.