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Thick/Thin Oxide Threshold Ratio for P Channel FETs

IP.com Disclosure Number: IPCOM000079021D
Original Publication Date: 1973-Apr-01
Included in the Prior Art Database: 2005-Feb-26
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Chin, WB: AUTHOR [+2]

Abstract

P Channel field-effect transistor (FET) devices by themselves or in complementary structures have a less favorable (smaller) ratio of thick oxide threshold voltage to thin oxide threshold voltage, as compared to corresponding with N Channel devices. This is especially harmful to design and application of dynamic memories.

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Thick/Thin Oxide Threshold Ratio for P Channel FETs

P Channel field-effect transistor (FET) devices by themselves or in complementary structures have a less favorable (smaller) ratio of thick oxide threshold voltage to thin oxide threshold voltage, as compared to corresponding with N Channel devices. This is especially harmful to design and application of dynamic memories.

In contrast, the illustrated structure calls for the formation of a more highly doped N layer at and near the silicon surface, in areas where thick oxide parasitic devices are possible. The N layer will be more highly doped than the N doping of the thin oxide FET channel regions. The N layer doping concentration and its insulator thickness (SiO(2), etc) are such that thick oxide threshold voltage will be at a desired level. The N layer doping concentration will also be such, that its breakdown voltage to the P source-drain regions will be above a desired level. The N layer can be formed either by diffusion or ion implant.

In operation, the N skin will increase the thick oxide threshold and subthreshold conduction voltages. Therefore, it will decrease the subthreshold conduction.

Thus, when the metal signal line is biased at -V, it will prevent the parasitic thick oxide FET between any two P+ diffusions from being turned on, to degrade the signals on the diffused signal line. This is especially true for dynamic circuits, where a charge stored at the P+ diffusion signal node will not be disturbed...