Operation, development and application of the velocity modulation transistor
Abstract
Transistors utilizing real space transfer (RST) have drawn significant attention because RST opens new avenues of transistor operation. They have potential for increased speed and functionality compared to conventional devices. The velocity modulation transistor (VMT) has a speed advantage over the high electron mobility transistor (HEMT) because its mode of switching differs. Rather than filling and emptying its primary conduction channel by moving carriers longitudinally from source to drain, carriers move transversely between high-speed and low-speed channels. Thus, the VMT can take advantage of epitaxially defined distances as opposed to lithographically defined distances. Epitaxially grown heterostructures have been designed and developed to support VMT technology. New dual- and triple-gated transistors have been developed in order to verify that electrons are actually moving between the two channels. Working VMTs have been designed, fabricated and tested in a GaAs/Al$\sb{x}$Ga$\sb{1-x}$As system. These transistors use a high mobility two-dimensional electron gas and a low mobility, doped channel to obtain a velocity differential between channels. Although an individual VMT is capable of faster switching than a HEMT of similar materials and equal lithographic feature sizes, the VMT circuit is limited to speeds which can be achieved by HEMT circuits in circuit applications where one transistor drives a similar transistor. Channel carrier population as a function of input gate voltage is calculated for HEMTs and VMTs using a 1-D model. The model is used to compare the equivalent circuits of HEMTs and VMTs to establish relative performances. The equivalent circuits are examined from driver and load perspectives. Applications in which the VMT's full switching speed can be utilized effectively are limited. These applications are discussed.
Degree
Ph.D.
Advisors
Webb, Purdue University.
Subject Area
Electrical engineering
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