THE ELECTRONIC SATURATED CARRIER VELOCITY EFFECT APPLIED TO A CURRENT LIMITER
A review of the electronic saturated carrier velocity effect is made and related to the application of this effect to the construction of a two terminal current limiting device in silicon material. A simple model of a current limiter device was made with the first evident problem of power dissipation solved through construction of devices having very high surface to volume ratios through the use of a small device structure. Devices were constructed based on the simple model. Testing of these devices resulted in unexplainable results with the performance being from fair to poor. An analytical explanation for the failure was found that consisted of a simple model of space charge injection. This model of space charge injection proved to be inadequate and was replaced by a computer model capable of solutions calculating the actual space charge distribution rather than being based on an assumed solution as the analytical model had been. A new set of test devices was constructed from improved materials and structures. The testing procedure was changed from steady state to pulse testing to reduce thermal effects. These devices performed as expected except for the avalanche failure which occurred at a lower level than expected. A review of the literature evoked one similar report of reduced avalanche voltage capability along with an accompanying analysis. The analysis was corrected for a mathematical error and an assumption of neglible space charge injection is shown to be in error by the computer analysis. The conclusion that the ionization rate must be higher at low fields than previously reported for n-type silicon is confirmed using the computer program. Although this dissertation resulted in much poorer current limiting devices than had originally been anticipated the understanding of the reasons for the failures aids future efforts by pointing out specific areas for improvement and providing a model as guidance for possible construction in other materials with better properties.
GORDON BARR SPELLMAN,
"THE ELECTRONIC SATURATED CARRIER VELOCITY EFFECT APPLIED TO A CURRENT LIMITER"
(January 1, 1982).
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