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

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

Mechanical properties of nano-silver joints as die attach materials

We achieve robust bonding of Cu wires to Cu pads on polyimide with silver nanopaste cured at 373 K. The paste is prepared by simply condensing Ag nanoparticle (NP) solution via centrifuging. The bonding is formed by solid state sintering of Ag NPs through neck growth and direct metallic bonding between clean Ag–Cu interfaces. Both experiment and Monte Carlo simulation confirm that the melting point of joint clusters increases during sintering. This creates improved bonds for use at an elevated operating temperature using Ag NPs.

Low temperature sintering of Ag nanoparticles for flexible electronics packaging

In order to take the full advantage of the high-temperature SiC and GaN operating devices, package materials able to withstand high-temperature storage and large thermal cycles have been investigated. The temperature under consideration here are higher than 200 °C. Such temperatures are required for several potential applications such as down-hole oil and gas industry for well logging, aircrafts, automotive, and space exploration. This review focuses on the reliability of a selection of potential components or materials used in the package assembly as the substrates, the die attaches, the interconnections, and the encapsulation materials. It reveals that, substrates with low coefficient of thermal expansion (CTE) conductors or with higher fracture resistant ceramics are potential candidates for high temperatures. Die attaches and interconnections reliable solutions are also available with the use of compatible metallization schemes. At this level, the reliability can also be improved by reducing the CTE mismatch between assembled materials. The encapsulation remains the most limiting packaging component since hard materials present thermomechanical reliability issues, while soft materials have low degradation temperatures. The review allows identifying reliable components and materials for high-temperature wide bandgap semiconductors and is expected to be very useful for researchers working for the development on high-temperature electronics.

Survey of High-Temperature Reliability of Power Electronics Packaging Components

Metal-metal bonding process using Ag metallo-organic nanoparticles

We have proposed a novel bonding process using silver nanoparticles, which can be alternative to lead-rich high melting point solders. The bonding mechanism of silver metallo-organic nanoparticles to bulk materials (gold and copper) is discussed based on the observations of the bonded interface using Transmission Electron Microscope (TEM). At the interface of sintered silver and bulk gold, the crystal orientation of silver corresponded to that of gold. It is thought that the epitaxial layer of silver formed through silver nanoparticles being oriented in the direction of the gold crystal. At the interface of sintered silver and bulk copper, no epitaxial layer of silver on the copper crystal formed. Though the appearance of the crystal structure of silver/copper interface is different from that of the silver/gold interface, copper as well as gold are coherent with silver, and have been successfully bonded using the silver nanoparticles. [doi:10.2320/matertrans.MF200805]

Interfacial Bonding Mechanism Using Silver Metallo-Organic Nanoparticles to Bulk Metals and Observation of Sintering Behavior

We investigated a new bonding technique utilizing micro-scaled silver-oxide (Ag 2 O) particles. The results of our investigations revealed that bonding between electrodes using for semiconductor modules can be accomplished by adding myristyl alcohol to silver-oxide particles, followed by heating the mixture in air at 300°C under a pressure of 2.5 MPa. Since this bonding technique produces silver particles with a size of a few nanometers when the silver oxide is reduced by the presence of the alcohol, low-temperature sintering and bonding can be achieved.

Bonding Technique Using Micro-Scaled Silver-Oxide Particles for In-Situ Formation of Silver Nanoparticles

We investigated a new bonding technique utilizing nano-scaled particles for use in high-temperature environments. The results of our investigations revealed that the method could be used to form bonds by simultaneously applying heat and pressure. Moreover, compared to a conventional Pb–5Sn-solder bond, a nanoparticle-based bond suffered no degradation in bonding strength over an elevated-temperature holding period of 1000 h at 250 °C, and its discharge characteristics were improved (i.e., increased) threefold. It is possible to extend this bonding technique to mounting components in devices that operate in high-temperature environments, e.g., it can be used to mount components such as silicon carbide (SiC) devices, which are expected to be applied in environments with temperatures exceeding 250 °C.

https://iopscience.iop.org/article/10.1143/JJAP.47.6615/pdf

Eiichi Ide

Papers

Metal-metal bonding process using Ag metallo-organic nanoparticles

Interfacial Bonding Mechanism Using Silver Metallo-Organic Nanoparticles to Bulk Metals and Observation of Sintering Behavior

Bonding Technique Using Micro-Scaled Silver-Oxide Particles for In-Situ Formation of Silver Nanoparticles

Study of Bonding Technology Using Silver Nanoparticles

Joint strength and interfacial microstructure between Sn–Ag–Cu and Sn–Zn–Bi solders and Cu substrate