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https://hdl.handle.net/2142/69254
Description
Title
Impact Ionization in Charge Coupled Devices
Author(s)
Detry, James Francis
Issue Date
1983
Department of Study
Electrical Engineering
Discipline
Electrical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Electronics and Electrical
Abstract
A charge coupled device was designed and fabricated for the purpose of measuring impact ionization at the silicon-silicon dioxide interface. All past experiments have measured impact ionization either totally or partly in the bulk. Since the mobility of holes and electrons is lower at the interface than in the bulk, the impact ionization coefficient should be different due to the increased scattering.
The CCD has no input or output circuitry but transferred the charge around a ring. Charge packets were thermally or optically generated and the device was operated at 77 K to prevent thermal generation during measurements. The CCD was a three phase surface channel device. The gates were aluminum with etched two micron gaps. The device was capable of operation with greater than 50 volts between the gates. At such high voltages the electric field in the silicon was high enough to cause impact ionization during charge transfer.
As the electrons of a partially full charge packet transferred across the gap, the additional electron produced by the ionization stayed with the packet while the hole was injected into the substrate. The impact ionization was to be measured by measuring the substrate current.
Experiments showed that the interface states were trapping the electrons and slowing the charge transfer so much that the substrate current due to impact ionization was below the threshold of measurement. An improved but much more complicated device is proposed for room temperature experiments which would minimize the effect of the interface states.
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