Integrated circuit with dynamic threshold voltage

Details Integrated circuit with dynamic threshold voltage Integrated circuit with dynamic threshold voltage

1999-06-21

2001-07-17

Dang, Trung (Department: 2823)

Semiconductor device manufacturing: process

Making field effect device having pair of active regions...

On insulating substrate or layer

C438S149000, C438S517000, C257S369000

Reexamination Certificate

active

06261878

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to integrated circuits and a method for making them.
BACKGROUND OF THE INVENTION
As transistor gate lengths continue to shrink, threshold voltages (V
t
) continue to decrease. Below 1.0 volts, it may become difficult to balance adequate current drive with acceptable leakage current. One way to address this problem is to design a device that has a dynamic threshold voltage, i.e., a device that has a lower V
t
when the device is turned on than when the device is turned off. By varying the threshold voltage in this way, even a low voltage device may provide a high drive current while continuing to maintain low subthreshold leakage.
Devices having a dynamic threshold voltage may be made by tying a body strap formed below the transistor's channel to the transistor's gate electrode, as described by Hu, et al., “A Dynamic Threshold Voltage MOSFET (DTMOS) for Ultra-Low Voltage Operation,” Int'l Electron Devices Meeting Technical Digest, 1994, pp. 809-812; and Hu et al., “Channel Profile Optimization and Device Design for Low-Power High-Performance Dynamic-Threshold MOSFET,” Int'l Electron Devices Meeting Technical Digest, 1996, pp. 113-116.
Such devices may use silicon-on-insulator (“SOI”) technology to electrically isolate the body strap from the junctions and adjacent transistors.
FIG. 1
illustrates such a device, which includes relatively thick silicon film
104
formed on oxide
103
. As shown, body strap
102
is separated from junctions
181
and
111
, which correspond to the lower boundaries for source
106
and drain
107
, respectively. Because of that separation, the capacitance that may result, when the device is turned on, can slow down the rate at which the body potential increases in response to an increase in the voltage applied to gate electrode
105
.
One way to address that problem is to use a relatively thin silicon layer instead of a relatively thick layer.
FIG. 2
illustrates such a device, which includes relatively thin silicon film
204
formed on oxide
203
. When a thin film is used, however, misalignment between body strap
202
and gate electrode
205
can cause a short circuit between body strap
202
and one of the junctions, e.g., junction
211
in the device shown here.
There is a need for a device that does not include such short circuits, or produce unacceptable capacitance that slows down the rate of body potential increase when the device is turned on. There is also a need for a method for making such a device.
SUMMARY OF THE INVENTION
An integrated circuit and method for making it are described. The integrated circuit includes a first insulating layer formed on a substrate and a body strap of a first conductivity type that is formed on the first insulating layer. A second insulating layer is formed on the first insulating layer adjacent to the body strap and a film is formed on the second insulating layer. A gate electrode is formed on the film and a plurality of doped regions of a second conductivity type are formed within the film that extend from the surface of the film to the surface of the second insulating layer. The doped regions have junctions that are each spaced from the body strap by at least about 500 angstroms.


REFERENCES:
patent: 5498882 (1996-03-01), Houston
patent: 5559368 (1996-09-01), Hu et al.
patent: 5753955 (1998-05-01), Fechner
patent: 5942781 (1999-08-01), Burr et al.
Hu et. al., “A Dynamic Threshold Voltage MOSFET (DTMOS) for Ultra-Low Voltage Operation”, Int'l Electron Dev. Meeting Technical Digest, pp 809-812, 1994.*
Hu et al., “Channel Profile Optimization and Device Design for Low-Power High-Performance Dynamic Threshold MOSFET”, Int'l Electron Devices Meeting Technical Digest, pp. 113-116, 1996.

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