Harleysville, PA, United States
Harleysville, PA, United States

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ROHM Semiconductor and MaxPower, Inc. | Date: 2016-08-23

A semiconductor device according to the present invention includes a semiconductor layer having a trench, a first insulating film formed along an inner surface of the trench, and an upper electrode and a lower electrode embedded in the trench via the first insulating film and disposed above and below a second insulating film. An electric field relaxation portion that relaxes an electric field arising between the upper electrode and the semiconductor layer is provided between a side surface of the trench and a lower end portion of the upper electrode.

MaxPower, Inc. | Date: 2016-07-05

In one embodiment, a RESURF structure between a source and a drain in a lateral MOSFET is formed in a trench having a flat bottom surface and angled sidewalls toward the source. Alternating P and N-type layers are epitaxially grown in the trench, and their charges balanced to achieve a high breakdown voltage. In the area of the source, the ends of the P and N-layers angle upward to the surface under the lateral gate and contact the body region. Thus, for an N-channel MOSFET, a positive gate voltage above the threshold forms a channel between the source and the N-layers in the RESURF structure as well as creates an inversion of the ends of the P-layers near the surface for low on-resistance. In another embodiment, the RESURF structure is vertically corrugated by being formed around trenches, thus extending the length of the RESURF structure for a higher breakdown voltage.

In one embodiment, a power MOSFET vertically conducts current. A bottom electrode may be connected to a positive voltage, and a top electrode may be connected to a low voltage, such as a load connected to ground. A gate and/or a field plate, such as polysilicon, is within a trench. The trench has a tapered oxide layer insulating the polysilicon from the silicon walls. The oxide is much thicker near the bottom of the trench than near the top to increase the breakdown voltage. The tapered oxide is formed by implanting nitrogen into the trench walls to form a tapered nitrogen dopant concentration. This forms a tapered silicon nitride layer after an anneal. The tapered silicon nitride variably inhibits oxide growth in a subsequent oxidation step.

Various improvements in vertical transistors, such as IGBTs, are disclosed. The improvements include forming periodic highly-doped p-type emitter dots in the top surface region of a growth substrate, followed by growing the various transistor layers, followed by grounding down the bottom surface of the substrate, followed by a wet etch of the bottom surface to expose the heavily doped p+ layer. A metal contact is then formed over the p+ layer. In another improvement, edge termination structures utilize p-dopants implanted in trenches to create deep p-regions for shaping the electric field, and shallow p-regions between the trenches for rapidly removing holes after turn-off. In another improvement, a dual buffer layer using an n-layer and distributed n+ regions improves breakdown voltage and saturation voltage. In another improvement, p-zones of different concentrations in a termination structure are formed by varying pitches of trenches. In another improvement, beveled saw streets increase breakdown voltage.

Lateral power devices where immobile electrostatic charge is emplaced in dielectric material adjoining the drift region. A shield gate is interposed between the gate electrode and the drain, to reduce the Miller charge. In some embodiments the gate electrode is a trench gate, and in such cases the shield electrode too is preferably vertically extended.

Agency: Department of Defense | Branch: Navy | Program: SBIR | Phase: Phase II | Award Amount: 742.38K | Year: 2016

MaxPower Inc. is proposing the continued development of a lithium reserve battery for air-to-surface missile (ASM) applications based on their missile operational environment validated Lithium/Vanadium Pentoxide technology. The basis for this Phase II effort is the Phase I work performed on reconfiguring a reserve battery, originally designed to meet the requirements of the reentry vehicle on the Minuteman III ICBM, to those of Navy long-range missile applications. The original battery met the electrical and safety requirements following environmental testing while also providing significant weight reductions when compared to the fielded Zinc/Silver Oxide system and the competing thermal battery. The development in the Phase I program demonstrated the battery systems ability to meet the ASM power and energy requirements via prototype cell testing. These tests led to a revised battery energy projection that surpassed the program goal of 200 Ws/g, with a projected mass of 7.9 lbs, well under the 13 lb maximum requirement. Phase II development work will focus on increasing battery design fidelity and validating the design via full battery testing with particular attention focused on low temperature performance. Prototype batteries will be built for internal functional testing and for delivery to the Navy for their testing.

In one embodiment, a power MOSFET cell includes an N+ silicon substrate having a drain electrode. An N-type drift layer is grown over the substrate. An N-type layer, having a higher dopant concentration than the drift region, is then formed along with a trench having sidewalls. A P-well is formed in the N-type layer, and an N+ source region is formed in the P-well. A gate is formed over the P-wells lateral channel and has a vertical extension into the trench. A positive gate voltage inverts the lateral channel and increases the vertical conduction along the sidewalls to reduce on-resistance. A vertical shield field plate is also located next to the sidewalls and may be connected to the gate. The field plate laterally depletes the N-type layer when the device is off to increase the breakdown voltage. A buried layer and sinker enable the use of a topside drain electrode.

N-channel power semiconductor devices in which an insulated field plate is coupled to the drift region, and immobile electrostatic charge is also present at the interface between the drift region and the insulation around the field plate. The electrostatic charge permits OFF-state voltage drop to occur near the source region, in addition to the voltage drop which occurs near the drain region (due to the presence of the field plate).

Reverse-conducting IGBTs where the collector side includes diode terminal regions, and the semiconductor material is much thicker through the diode terminal regions than it is through the collector regions. This exploits the area fraction which is taken up by the diode terminal regions to provide increased rigidity for the wafer, and thus avoid warping.

MaxPower, Inc. | Date: 2016-02-01

Power semiconductor devices, and related methods, where majority carrier flow is divided into paralleled flows through two drift regions of opposite conductivity types.

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