High Ion/Ioff SOI MOSFET using body voltage control
View Patent ↗A semiconductor device may comprise a partially-depleted SOI MOSFET having a floating body region disposed between a source and drain. The floating body region may be driven to receive injected carriers for adjusting its potential during operation of the MOSFET. In a particular case, the MOSFET may comprise another region of semiconductor material in contiguous relationship with a drain/source region of the MOSFET and on a side thereof opposite to the body region. This additional region may be formed with a conductivity of type opposite the drain/source, and may establish an effective bipolar device per the body, the drain/source and the additional region. The geometries and doping thereof may be designed to establish a transport gain of magnitude sufficient to assist the injection of carriers into the floating body region, yet small enough to guard against inter-latching with the MOSFET.
1. A semiconductor device comprising:
a layer of semiconductor material over an insulator;
a source region, a body region and a drain region for a Metal-Oxide Semiconductor Field Effect Transistor (MOSFET) formed in the layer of semiconductor material;
the drain region and the source region each comprising a conductivity of first-type;
the body region comprising a conductivity of second-type, the second-type opposite to the first-type;
a gate disposed over the body region and configured to be operable when under bias to form a conductive channel in a partial thickness of the body region between the drain region and the source region, a further thickness of the body region other than the partial thickness defining at least in part a floating body region of the body region; and
another doped region of the conductivity of the second-type contacting the drain region, the drain region in contiguous and electrical series relationship between the body region and the another doped region;
the body region, the drain region and the another doped region respectively configured to be operable collectively as an inherent bipolar device with a carrier transport gain sufficiently great to assist injection of carriers into the floating body region of the body region to impart an operable dynamic-kink effect to the MOSFET, yet sufficiently small to avoid inducing latching of the MOSFET with the another doped region when collectively in operation.
2. The semiconductor device of claim 1 , in which
the drain region comprises doping attributable to a base region for the inherent bipolar device;
the another doped region comprises doping attributable to an emitter region for the inherent bipolar device; and
the doping for the base region over a base integral length thereof relative to the doping for the emitter region over an emitter integral length thereof that define a ratio therebetween of magnitude to establish the carrier transport gain for the inherent bipolar device.
3. The semiconductor device of claim 2 , further comprising silicide over the drain region to affect at least in part a recombination rate for minority carriers in the base region.
4. The semiconductor device of claim 1 , further comprising first silicide over a region of the another doped region, the first silicide defining an outline that is offset laterally clear of a boundary defined between the drain region and the another doped region.
5. The semiconductor device of claim 4 , in which the first silicide is connected to a circuit node operably configured to receive when the device is operating a bias for enabling collectively with the gain of the inherent bipolar device the injection of minority carriers into the base region of the inherent bipolar device and into the floating body of the MOSFET.
6. The semiconductor device of claim 4 , further comprising second silicide separate from the first silicide over a region of the drain region, in which the second silicide defines an outline that is offset laterally clear of the boundary between the drain region and the another doped region and offset laterally clear of the gate.
7. The semiconductor device of claim 1 , in which the drain region comprises a first doping concentration in a lower region thereof proximate the insulator and a second doping concentration in an upper region thereof proximate a surface of the layer of semiconductor material;
the second concentration greater than the first concentration by at least a factor of two.
8. The semiconductor device of claim 1 , in which
the drain region comprises a first doping concentration in a lower region thereof proximate the insulator and a second doping concentration in an upper region thereof proximate a surface of the layer of semiconductor material; and
the first concentration is greater that the second concentration by at least a factor of two.
9. The semiconductor device of claim 1 , in which
the source, the body and the drain regions define at least in part a silicon-on-insulator (SOI) partially-depleted MOSFET; and
the another doped region is operatively configured relative to and collectively with the drain region to enable, when the device is operating, variation of a V t characteristics of the MOSFET by injection of carriers into the floating body, the variation of magnitude sufficient to impart a subthreshold swing to the MOSFET of magnitude less than 60 mV at room temperature.