Reducing the Cost of Vertical MOSFETs Using Laser Dicing Technology--GaN WAFER

GaN Vertical MOSFETs are promising power devices for electric vehicles, surpassing similar SiC devices in terms of channel mobility, a key metric. However, the high cost of native substrates has hindered their commercial success.

To address this issue, various teams have been investigating GaN substrate recycling technologies. Among these, a collaborative team consisting of researchers from Mirise Technologies, Nagoya University, and Hamamatsu has claimed to have conducted the most comprehensive demonstration of this method's success.

According to Takashi Ishida, a spokesperson for the Mirise team, previous reports on GaN substrate recycling were limited to evaluating parts of the process. Ishida states, "It is essential to evaluate the characteristics of devices manufactured on recycled wafers. Our paper is the first to report these results."

Ishida adds that while their results are encouraging, more work is needed before this process can be applied on an industrial scale. Since GaN substrates need to be recycled multiple times to reduce manufacturing costs, it is necessary to demonstrate that the devices grown on substrates after multiple rounds of recycling are not adversely affected.

As shown in the figure, the Japanese collaborative team's recycling process involves using a 532 nm laser to separate devices from the substrate. This light source irradiates the substrate from the N-face, and through two-photon absorption at the focal plane, the substrate decomposes into metallic gallium and nitrogen.

After separation, the N-face of the chips is polished to achieve a smooth surface, followed by metal deposition and packaging.

The Ga-face of the released substrate is first polished, then chemically mechanically polished to achieve atomic-level flatness, and then HVPE is used to deposit a GaN layer approximately 90 μm thick. According to the team, after this additional chemical mechanical polishing step, the GaN substrate appears as good as new.

To evaluate their process, the research team measured the performance of lateral MOSFETs and vertical p-n diodes fabricated on the same wafer. Both types of devices were formed from epitaxial wafers produced in the MOCVD process: first, a 4 μm thick n-type GaN layer doped at 1 x 10^17 cm^-3, followed by a 2 μm thick p-type GaN layer doped at 5 x 10^17 cm^-3.

The study first assessed the performance of both types of devices before and after GaN substrate dicing. Graphs of MOSFET drain current and gate current at different gate voltages and diode reverse current at different reverse bias values showed no significant changes due to laser dicing. This led the research team to conclude that the devices were "barely affected" by the dicing process, as the laser source's heating and the stresses related to the separation step could have had an impact.

Takashi Ishida and his colleagues compared these measurements with those of lateral MOSFETs and vertical p-n diodes produced using recycled substrates. The results were very similar, with a difference in gate leakage current for the lateral MOSFETs, attributed to variations in gate insulator quality.

According to the research team, their findings indicate that the performance of devices did not significantly degrade after the GaN recycling process.

Takashi Ishida states that besides recycling GaN substrates, increasing their size is necessary to make device production costs more competitive. The research team is interested in demonstrating their recycling process using larger GaN substrates.

This highlights the advantages of GaN substrates.

• High Breakdown Voltage: GaN substrates can handle high voltages, making them ideal for high-power applications.
• High Electron Mobility: GaN substrates exhibit high electron mobility, which contributes to faster switching speeds and higher efficiency.
• Wide Bandgap: GaN has a wide bandgap, allowing devices to operate at higher temperatures and voltages compared to silicon-based devices.
• High Thermal Conductivity: GaN substrates have superior thermal conductivity, which helps in efficient heat dissipation and enhances device reliability.
• Low On-Resistance: Devices built on GaN substrates typically have lower on-resistance, leading to lower conduction losses and improved overall performance.
• High Frequency Capability: GaN substrates are suitable for high-frequency applications, including RF and microwave communications.
• Robustness: GaN devices are more robust and can withstand harsh environmental conditions, making them suitable for demanding applications.
• Reduced Size and Weight: GaN-based devices can be smaller and lighter than their silicon counterparts, which is beneficial in applications where space and weight are critical.
• Improved Efficiency: The inherent properties of GaN lead to improved efficiency in power conversion, which is crucial for applications like electric vehicles and renewable energy systems.
• Enhanced Performance in High-Temperature Environments: GaN substrates perform well in high-temperature environments, maintaining their efficiency and reliability.
• Potential for Cost Reduction: As recycling and manufacturing processes for GaN substrates improve, the cost can be reduced, making GaN-based devices more commercially viable.
• Compatibility with Advanced Fabrication Techniques: GaN substrates can be integrated with advanced fabrication techniques, such as laser dicing, to further enhance device performance and reduce production costs.

GaN we can provide

GaN Gallium Nitride Wafer High Electron Mobility RF Devices Optoelectronics And LEDs(click the picture for more)

Gallium Nitride (GaN) wafers have emerged as a pivotal technology in various industries, owing to their unique material properties. With a wide bandgap, high electron mobility, and exceptional thermal stability, GaN wafers find applications in power electronics, RF devices, optoelectronics, and more. This abstract explores the versatile applications of GaN wafers, from powering 5G communications to illuminating LEDs and advancing solar energy systems. The high-performance characteristics of GaN make it a cornerstone in the development of compact and efficient electronic devices, influencing sectors such as automotive electronics, aerospace, and renewable energy. As a driving force in technological innovation, GaN wafers continue to redefine possibilities across diverse industries, shaping the landscape of modern electronics and communication systems.