PUNCH-THROUGH SPACE-CHARGE LIMITED LOADS (RESISTORS).

Abstract

There are several important semiconductor devices in which the transport of carriers is controlled by punch-through space-charge effects. Examples include the Bipolar Mode Static Induction Transistor (BSIT), ultrasmall Punch-through MOSFETs, and BARITT diodes for microwave applications. The development of punch-through space-charge type of devices is a technology motivated by the demanding high density among the IC chips. This dissertation discusses a device which operates in a punch-through condition with space-charge control of currents. It is a two terminal device, which could be fabricated with no deviation from today's technology. The device structure is simple, with two n⁺ or p⁺ regions formed in p⁻ or n⁻ substrate, respectively. Punch-through space-charge limited structures both n⁺p⁻n⁺ and p⁺n⁻p⁺, were simulated using a general one-dimensional semiconductor device performance simulation program GESIM1 for dynamic and static analysis. The results of simulation show that the potential barrier height decreases with increasing applied potential and with a reduction of the spacing L between the n⁺ diffusion in an n⁺p⁻n⁺ structure. The resistance increases as the spacing L is increased. A two-dimensional analytical model of carrier transport in the device was developed. This model accounts for surface effects as well as the space-charge limited flow. Also, a one-dimensional model that includes mobile carriers effects on the device operation. Structures of various configurations were fabricated and tested. Electrical evaluations of these structures provided large value resistors in a remarkably small area compare to traditional integrated resistors. The resistance was observed to increase with the spacing L and with the resistivity of the starting substrate. These punch-through space-charge limited loads should have applications as an alternative approach for integrated resistors in high-speed VLSI applications. They can provide very small area, large value resistors based on the space-charge limiting action of the device. The range of resistance value is large, and small dimensions lead to small capacitance and fast switching times.