Manufacturing Bits: Jan. 3

Gallium oxide chips
Looking to commercialize a promising ultra wide-bandgap technology in the market, Novel Crystal Technology (NCT) has developed a Schottky barrier diode based on a material called gallium oxide.

NCT devised an ampere-class 1,200-V diode based on gallium oxide. A diode is a device that passes electricity in one direction and blocks it in the opposite direction. Still in R&D, devices based on gallium oxide promise to pave the way towards lower priced and higher performance power semiconductors. Gallium oxide devices are geared for use in fast charging applications, electric vehicles (EVs), solar, trains and even flying cars.

For some time, NCT and others have been developing power devices based on gallium oxide, an ultra wide-band technology that consists of better material properties than silicon, silicon carbide (SiC) or gallium nitride (GaN). But gallium oxide devices will also face challenges in moving from the lab to the fab.

Power semiconductors in general are specialized transistors, which operate as a switch in high-voltage applications such as automotive, power supplies, solar, and trains. The devices allow the electricity to flow in the “on” state, and stop it in the “off” state. They boost the efficiencies and minimize the energy losses in systems.

For years, the power semiconductor market has been dominated by silicon-based devices like IGBTs and power MOSFETs. These power devices are mature and inexpensive, but they also are reaching their theoretical limits.

That’s why there is a keen interest in devices using wide-bandgap materials, which can exceed the performance of today’s silicon-based devices. For years, vendors have been shipping power semi devices based on two wide-bandgap technologies—GaN and SiC.

Meanwhile, several companies, government agencies, R&D organizations and universities are working on beta gallium oxide (β-Ga2O3), a promising ultra wide-bandgap technology that’s been in R&D for several years. “The electronic bandgap is the energy gap between the top of the valence band and the bottom of the conduction band in solid materials,” according to Mouser Electronics in a blog. “It is the bandgap that gives semiconductors the ability to switch currents on and off as desired in order to achieve a given electrical function.”

Gallium oxide, an inorganic compound, has a bandgap from 4.8 to 4.9 eV, which is 3,000 times greater than silicon, 8 times greater than SiC, and 4 times greater than GaN, according to Kyma, a supplier of power devices and wafers. Gallium oxide also exhibits a high breakdown field of 8MV/cm and good electron mobility, according to Kyma.

Gallium oxide also has a less costly crystal growth method than SiC and GaN, making it easier to develop wafers. But the technology also has some challenges, which is why is still in the R&D phase.

NCT plans to commercialize the technology. Using its research prototype production line, the company has developed a mass-production process for trench-type diodes on 2-inch wafers. It has developed the first ampere-class 1,200-V breakdown-voltage diodes based on the technology.

The company plans to establish a manufacturing process for these devices, aiming for commercialization in 2023. It has built a 100mm foundry line for gallium oxide epitaxial wafers, which started to go on sale in 2021.

GaO photodetectors
The University of Science and Technology of China (USTC) of the Chinese Academy of Sciences has developed solar-blind ultraviolet photodetectors using amorphous gallium oxide.

SBPDs based on gallium oxide are potential candidates for harsh environments, such as space exploration and other applications. These devices could be used in systems for rapid flame detection and early fire warning applications.

A photodetector is a device which is used for the detection of light. There are many types of photodetectors, including photodiodes, according to the RP Photonics Encyclopedia. “Photodiodes are semiconductor devices with a p–n junction or p–i–n structure,” according to the web site.

Solar-blind photodetectors are insensitive to infrared, visible and near-UV light. But these devices respond to ultraviolet light with wavelengths below about 300nm, according to the web site. “Solar-blind detectors are interesting for all applications where one needs to detect ultraviolet light while not being disturbed by (possibly much stronger) visible light,” according to the site.

In space and related applications, these devices must withstand harsh environments like high temperature and radiation.
In some cases, SBPDs are made using silicon substrates, which may not withstand harsh conditions. So, researchers are looking at SBPDs using wide-band gap technologies like GaN and SiC.

USTC developed ultra-sensitive SBPDs using gallium oxide. Researchers developed a defect and doping (DD) technology for amorphous gallium oxide materials to operate in harsh conditions. The materials have a high responsivity rejection ratio. “SBPDs based on DD engineering showed good performance such as high resistance. Devices under engineering processes showed superior spectrum-selectiveness in many aspects, and sharp sensitivity under extreme conditions,” according to researchers.

Pure GaAs
Princeton University has developed a device based on the world’s purest sample of gallium arsenide (GaAs).

Researchers developed a GaAs material with only one impurity for every 10 billion atoms. GaAs is not new and is widely used in many systems. For example, small GaAs-based power amplifiers are used in today’s smartphones.

Princeton devised an ultra-pure material, which formed the basis of a GaAs device. Researchers took the device and subjected it to cold temperatures. Then, they subjected it to a magnetic field and applied a voltage. This, in turn, sent electrons through a two-dimensional plane sandwiched between the material’s crystalline layers.

When they lowered the magnetic field, they found a surprising series of effects. In operation, the electrons aligned into a lattice structure known as a Wigner crystal. A Wigner crystal is the solid crystalline phase of electrons, according to Wikipedia.

“Scientists previously thought Wigner crystals required extremely intense magnetic fields,” according to researchers from Princeton. “The results, published in Nature Materials, showed that many of the phenomena driving today’s most advanced physics can be observed under far weaker magnetic fields than previously thought. Lower magnetic fields could empower more labs to study the mysterious physics problems buried within such two-dimensional systems. These less severe conditions present physics that have no established theoretical framework, paving the way for further exploration of quantum phenomena.”