There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

An object is to provide a semiconductor device of which a manufacturing process is not complicated and by which cost can be suppressed, by forming a thin film transistor using an oxide semiconductor film typified by zinc oxide, and a manufacturing method thereof. For the semiconductor device, a gate electrode is formed over a substrate; a gate insulating film is formed covering the gate electrode; an oxide semiconductor film is formed over the gate insulating film; and a first conductive film and a second conductive film are formed over the oxide semiconductor film. The oxide semiconductor film has at least a crystallized region in a channel region.

Semiconductor device, and manufacturing method thereof

Various embodiments for improved power devices as well as their methods of manufacture, packaging and circuitry incorporating the same for use in a wide variety of power electronic applications are disclosed. One aspect of the invention combines a number of charge balancing techniques and other techniques for reducing parasitic capacitance to arrive at different embodiments for power devices with improved voltage performance, higher switching speed, and lower on-resistance. Another aspect of the invention provides improved termination structures for low, medium and high voltage devices. Improved methods of fabrication for power devices are provided according to other aspects of the invention. Improvements to specific processing steps, such as formation of trenches, formation of dielectric layers inside trenches, formation of mesa structures and processes for reducing substrate thickness, among others, are presented. According to another aspect of the invention, charge balanced power devices incorporate temperature and current sensing elements such as diodes on the same die. Other aspects of the invention improve equivalent series resistance (ESR) for power devices, incorporate additional circuitry on the same chip as the power device and provide improvements to the packaging of charge balanced power devices.

Power semiconductor devices and methods of manufacture

A power semiconductor device includes trenches disposed in a first base layer of a first conductivity type at intervals to partition main and dummy cells, at a position remote from a collector layer of a second conductivity type. In the main cell, a second base layer of the second conductivity type, and an emitter layer of the first conductivity type are disposed. In the dummy cell, a buffer layer of the second conductivity type is disposed. A gate electrode is disposed, through a gate insulating film, in a trench adjacent to the main cell. A buffer resistor having an infinitely large resistance value is inserted between the buffer layer and emitter electrode. The dummy cell is provided with an inhibiting structure to reduce carriers of the second conductivity type to flow to and accumulate in the buffer layer from the collector layer.

Power semiconductor device

Recent success with the fabrication of high-performance GaN-on-Si high-voltage HFETs has made this technology a contender for power electronic applications. This paper discusses the properties of GaN that make it an attractive alternative to established silicon and emerging SiC power devices. Progress in development of vertical power devices from bulk GaN is reviewed followed by analysis of the prospects for GaN-on-Si HFET structures. Challenges and innovative solutions to creating enhancement-mode power switches are reviewed.

https://iopscience.iop.org/article/10.1088/0268-1242/28/7/074011/pdf

Gallium nitride devices for power electronic applications

It is widely recognized that Hybrid Vehicles (HVs) are suitable for solving problems of energy saving and reduction of CO2 emission. For the future system, higher performance power devices superior to Si-IGBT, which is used for present HVs, are strongly required. GaN is the promising material for post Si power devices. We are developing GaN power switching devices. For high power switching devices, two types of vertical device structure have been developed. One is similar to double diffused MOSFET of Si. The other type is U-shape trench gate MOSFET. Both types of the power device have now insufficient performances for the applications. However, GaN has shown the potential as the post Si materials of high power devices.

GaN Power Switching Devices for Automotive Applications

A semiconductor device containing a lateral MOS transistor comprising a silicon substrate, an n-type first semiconductor layer constituting a drain drift region, a p-type second semiconductor layer prepared within the first semiconductor layer to constitute a body region and with a channel region formed within a portion of said body region, an n-type third semiconductor layer prepared on the surface of the second semiconductor layer to constitute a source region, an n-type fourth semiconductor layer constituting a drain region, and an insulation layer that is constituted of insulating material filled into a trench prepared in the first semiconductor layer and arranged along the two sides of the drain region. The drain region is formed into a region deeper than the insulation layer and in contact with the drain drift region at a portion beneath the insulation layer. The semiconductor device provides a high breakdown voltage and a low on-resistance, and can be fabricated with a reduced cell pitch.

Semiconductor device with a high breakdown voltage,low on-resistance,lateral power mosfet

The effects of the Cl2-based inductively coupled plasma (ICP) etching of GaN on the interface properties of Al2O3/GaN structures prepared by atomic layer deposition (ALD) were investigated. We used n-GaN layers grown on freestanding n+-GaN substrates with low dislocation density. The ICP etching caused slight disorder of the chemical bonds at the GaN surface and monolayer-level interface roughness at the Al2O3/GaN interface, resulting in poor capacitance–voltage (C–V) characteristics due to high-density interface states including nitrogen-vacancy (VN) related levels. The postannealing process in N2 at 400 °C drastically improved the C–V characteristics, probably owing to the partial recovery of the VN-related defects and the increased ordering of chemical bonds in the GaN surface region.

https://iopscience.iop.org/article/10.1143/JJAP.51.060201/pdf

Interface Properties of Al2O3/n-GaN Structures with Inductively Coupled Plasma Etching of GaN Surfaces

Photocurrent induced by sub-bandgap light absorption due to the Franz-Keldysh effect was observed in GaN p-n junction diodes under a high reverse bias voltage. The photocurrent increased with the reverse bias voltage and the increase was found to be more significant as the wavelength approached the absorption edge of GaN. The photocurrent was calculated with consideration of light absorption induced by the Franz-Keldysh effect in the depletion layer. The calculated curves showed excellent agreement with the experimental curves. The photocurrent also increased with an increase in temperature and this could be quantitatively explained by the red-shift of the GaN absorption edge with the increase in temperature.Photocurrent induced by sub-bandgap light absorption due to the Franz-Keldysh effect was observed in GaN p-n junction diodes under a high reverse bias voltage. The photocurrent increased with the reverse bias voltage and the increase was found to be more significant as the wavelength approached the absorption edge of GaN. The photocurrent was calculated with consideration of light absorption induced by the Franz-Keldysh effect in the depletion layer. The calculated curves showed excellent agreement with the experimental curves. The photocurrent also increased with an increase in temperature and this could be quantitatively explained by the red-shift of the GaN absorption edge with the increase in temperature.

Franz-Keldysh effect in GaN p-n junction diode under high reverse bias voltage

The improvement of current collapses of p-GaN gate GaN high-electron-mobility transistors (HEMTs) caused by the effects of surface treatment and the passivation layer was investigated. The NH3 treatment and high-temperature oxide (HTO) passivation layer on the AlGaN layer are effective in improving the current collapse of a p-GaN gate GaN HEMT. The current collapse at a long time constant (τ= 4 s) could be decreased by the NH3 treatment of the AlGaN layer, because the nitrogen atoms in nitrogen vacancies in the AlGaN layer (trap level: 0.6 eV) would be incorporated, resulting in a low surface density. The current collapse at an intermediate time constant (τ= 11 ms) could also be decreased by the deposition of the HTO passivation layer on the AlGaN layer, because the low-interface-density layer (trap level: 0.4 eV) of HTO/AlGaN would be formed.

https://iopscience.iop.org/article/10.7567/JJAP.52.04CF08/pdf

Tsutomu Uesugi

Papers

GaN Power Switching Devices for Automotive Applications

Semiconductor device with a high breakdown voltage,low on-resistance,lateral power mosfet

Interface Properties of Al2O3/n-GaN Structures with Inductively Coupled Plasma Etching of GaN Surfaces

Franz-Keldysh effect in GaN p-n junction diode under high reverse bias voltage

Improvement of Current Collapse by Surface Treatment and Passivation Layer in p-GaN Gate GaN High-Electron-Mobility Transistors