Electrical Specifications of Extrinsic Threshold Devices

Various matrix addressing schemes are possible with two- and three-terminal devices. For more information, the reader is referred to an early paper of the RCA group (Lechner et al., 1971). Matrix addressing differs from multiplexing in that the LC can be driven at 100% duty factor, maintaining superior optical performance. 

Numerical evaluations, with A = 0.01, show that very large arrays (Nm 1000) can be addressed for n 10. 

In practical devices, just as in the case of the varistor, Nm is usually limited by the capacitance of the diode, rather than by its static behavior. An evaluation of the diode shows that its minimum size is set by lithography, rather than by current density considerations. A small (2 X 2-jim) back-to-back diode, fabricated in a 5000-A-thick amorphous Si film has a capacitance in the order of 10-3 pF. The impedance of this capacitance limits the maximum number of lines that can be addressed. It appears that large displays, several hundred lines, can be addressed since the typical capacitance of a 1 X 1-mm LCD cell is about 10 pF. 

The chief advantage of BTBDs is their simple construction. Unlike the TFT, no dielectric layer is required. Since failure of the gate dielectric is the chief cause of low yield, BTBD-controlled matrix displays should have higher yields. 

Amorphous Si H has an effective-field drift mobility about 0.2 cm2 V-1 sec-1. To gain some perspective on how this material might fit into active matrix display applications, the requirements on a TFT designed to drive a 1-mm2 GH LCD pixel will be discussed. In the linear regime, the transistor can be modeled as a (gate-voltage-controlled) resistor, and the minimum ON resistance Rmi is approximately given by the estimate 

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