Abstract
In recent years, semiconductor manufacturers have been able to steadily reduce the physical area required by devices, thus allowing an increasing number of circuit functions on a single chip. Smaller semiconductor devices require more detailed and accurate analysis because minor errors can degrade their performance substantially.A new, completely numerical three-dimensional model of a MOSFET allows a unified treatment of small devices. Preliminary results show that device size effects the surface potential and threshold voltage. Classical theory does not predict these effects. Although the model currently converges slowly, it can still be useful in analysing new small geometry devices.
Highlights
The field effect transistor is a semiconductor device which depends for its operation on the control of current by an electric field
The first is its physical size; the metal oxide semiconductor FET (MOSFET) is so small compared to the BJT that it occupies only 20 to 30 per cent of the chip area taken up by a BJT
MOSFETs can be packed quite densely on an IC chip and they are widely used for large scale integration (LSI)
Summary
The field effect transistor is a semiconductor device which depends for its operation on the control of current by an electric field. This means that the time constant of the input circuit is long enough to enable the charge stored on the small capacitance to remain sufficiently long for the device to be useful as a storage element in digital circuits Another important property is that over a portion of their operating range they act like voltage controlled resistance elements and occupy much less area on the chip than the corresponding IC resistor. A MOSFET is considered small when its length and width have been shrunk to within an order of magnitude of the depth of the depletion region For such small geometry MOSFETs, the third dimension has an important role in the overall device performance.
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