Modeling the operation of the n-channel deep-depletion SOS/MOSFET

We present a model for the n-channel deep-depletion SOS/MOSFET which is valid over its entire operating range. This model, which is suitable for incorporation in a circuit simulation program, accurately predicts the source-to-drain current for device operation in depletion and in both weak and strong accumulation. Important aspects of the theory are 1) incorporation of the effect of the depth dependence of mobility in thin SOS films by computing accumulation layer thickness, 2) use of a computationally efficient approximation for silicon surface potential in accumulation, 3) inclusion of carrier velocity saturation effects on drain saturation potential, and 4) prediction of drain current in saturation through analysis of the velocity-saturated region of the channel. Verification of the model is achieved by comparing predicted drain current to that measured from test transistors of varying channel lengths (2.5-7.5 µm) and manufacture. The procedures used to obtain the model parameters from these devices are also included.