Steven Hung shung at cvd.Stanford.EDU
Fri Jun 8 10:12:54 PDT 2001

>Special University Ph.D. Seminar
>Exploration of Novel Gate Materials and Structures
>for MOS Applications
>Steven C.H. Hung
>Solid Sate Electronics Laboratory
>Stanford University
>June 8th    2pm
>CISX Auditorium, Room 101-X
>Heavily-doped polysilicon has long been the industry standard for the
>gate material in CMOS technology. However, several issues limit its
>performance as devices are scaled below 100 nm.  For example,
>limitations on carrier density (~ 1E20 cm-3) cause gate depletion
>effects which significantly degrade current drive improvements as gate
>oxide thickness is scaled.  In addition to such limitations, the
>polysilicon workfunction is essentially fixed, while an adjustable
>workfunction would provide device design flexibility and benefits for
>CMOS technology. The goal of this work is to explore alternative gate
>materials and structures that address the issues faced by polysilicon
>gates, specifically reducing gate depletion and enabling adjustment of
>the effective gate workfunction.
>The first portion of the talk will cover experimental work on a novel
>gate material, polycrystalline graphite (polycarbon). Polycarbon is a
>semimetallic substance with high carrier concentration (? 1021 cm-3).
>Analysis of polycarbon’s physical and electrical properties will be
>discussed.  The ability to tune the bulk polycarbon workfunction over a

>range of roughly +/- 0.3V around Si mid-gap, by adjusting deposition
>conditions, is demonstrated.  The second portion of the talk will cover

>a novel gate structure, which enables a wide range of effective
>workfunctions to be achieved for metallic gates, while suppressing gate

>depletion effects.

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