Browse Prior Art Database

Trench-Defined Capacitor

IP.com Disclosure Number: IPCOM000041944D
Original Publication Date: 1984-Mar-01
Included in the Prior Art Database: 2005-Feb-03
Document File: 2 page(s) / 40K

Publishing Venue

IBM

Related People

Culican, EF: AUTHOR [+3]

Abstract

In previously developed technologies, device capacitances were usually sufficiently large to slow down input/output (I/O) circuits. In those cases where more capacitance was needed, it could efficiently be obtained by using the capacitance of a charge-coupled storage (CCS) device or the capacitance due to the first metal level over a base diffusion. With the introduction of trench-defined transistors, CCS capacitance has been reduced significantly and the planarization techniques used for contact to first metal have minimized the base diffusion to first metal level capacitance. Accordingly, the problems of circuit design for I/O circuits in certain environments have been magnified. A desired capacitance value in a trench process involving regular devices can be achieved, but the area impact is significant in so doing. Fig.

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Trench-Defined Capacitor

In previously developed technologies, device capacitances were usually sufficiently large to slow down input/output (I/O) circuits. In those cases where more capacitance was needed, it could efficiently be obtained by using the capacitance of a charge-coupled storage (CCS) device or the capacitance due to the first metal level over a base diffusion. With the introduction of trench-defined transistors, CCS capacitance has been reduced significantly and the planarization techniques used for contact to first metal have minimized the base diffusion to first metal level capacitance. Accordingly, the problems of circuit design for I/O circuits in certain environments have been magnified. A desired capacitance value in a trench process involving regular devices can be achieved, but the area impact is significant in so doing. Fig. 1 illustrates a cross section of the known device, and Fig. 2 the trench-defined capacitor device. The key to the trench-defined capacitor is that the emitter diffusion and base diffusion butt the reach-through trench; moreover, the emitter has been enlarged. This maximizes the potential capacitance area and capacitance. The general rules, which must be followed to preclude the diffusion from shorting or spreading into the next device, are not violated here. The trench-defined capacitor has a value of approximately 3.2 pf and can be adjusted by geometry. The known device in this same area would yield approximately 0.06...