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FET Having Stepped Gate Oxide

IP.com Disclosure Number: IPCOM000080069D
Original Publication Date: 1973-Oct-01
Included in the Prior Art Database: 2005-Feb-26
Document File: 2 page(s) / 53K

Publishing Venue

IBM

Related People

Dockerty, RC: AUTHOR

Abstract

The use of a gate dielectric having two different thicknesses improves the gate reliability and the gain of a high-voltage field-effect transistor (FET) inverter circuit. Fig. 1 shows a schematic representation of a conventional field-effect transistor inverter circuit. Fig. 2 shows in cross-section a preferred structure which improves gate reliability and performance of the inverter circuit, by using a relatively thick gate dielectric in the portions of the FET channel which are exposed to high-electric fields.

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FET Having Stepped Gate Oxide

The use of a gate dielectric having two different thicknesses improves the gate reliability and the gain of a high-voltage field-effect transistor (FET) inverter circuit. Fig. 1 shows a schematic representation of a conventional field-effect transistor inverter circuit. Fig. 2 shows in cross-section a preferred structure which improves gate reliability and performance of the inverter circuit, by using a relatively thick gate dielectric in the portions of the FET channel which are exposed to high-electric fields.

With a high voltage applied to terminal V(h) and a voltage above threshold being applied to terminal V(in), the output voltage at terminal V(out) is at a relatively low value and a region of high gate electric field exists between gate G1 and N+ diffusion 2. When a potential below the threshold voltage is applied to terminal V(in), the output voltage at terminal V(out) is relatively high and a region of high gate electric field exists between gate G2 and N+ diffusion 2.

Accordingly, the thickness of the gate dielectric over the channel portions L2' of the load device and L2 of the active device which are adjacent to the N+ diffusion 2, is given the thick value T2 relative to the thin value T1 for the remaining channel portions L1' and L1, respectively, of the load and driver FET devices. The stepped gate oxide provides FET gain above that which results when the gate oxide is uniformly thick, that is, T2 for both the load and...