Radiation hardened GaN HEMT

It is reported that engineers from Nanjing University and Jiangsu Nenghua Microelectronics have collaborated to achieve strong radiation hardness in the new p-GaN HEMT, thus achieving a new breakthrough.

Team spokesperson Feng Zhou from Nanjing University stated that this achievement will open up a lucrative new market for GaN HEMTs. Feng Zhou believes that GaN devices have a very broad market in radiation environments, with a market size that can reach hundreds of millions of dollars or even more He stated that advanced wide bandgap semiconductors are urgently needed for orbiting satellites, spacecraft, and weapon facilities.

To demonstrate the excellent radiation hardness of their p-GaN HEMT and its ability to eliminate accumulated holes under radiation, Feng Zhou and colleagues compared their device with traditional GaN HEMTs using the single particle burn out value at a transmission line density of approximately 78 MeV cm2 mg-1. The energy transmission line density refers to the average radiation energy consumed by ionized particles on their unit length tracks.

Feng Zhou explained, "The density of transmission lines describes the energy consumption density of a specific type of radiation, which largely determines the adverse consequences of radiation exposure, such as electrical performance degradation and radiation damage

Another important aspect of the research conducted by Feng Zhou and his colleagues is the development of a UV pulse laser irradiation system that can evaluate the dynamic characteristics of devices by integrating power switch circuits. Feng Zhou stated that this new method of replacing heavy ion accelerators has achieved the first measurement of evaluating the power conversion efficiency of GaN power devices under radiation conditions.

Before manufacturing their p-GaN HEMT, Feng Zhou and his colleagues modeled the traditional form of this device. They found that due to the reverse blocking of the p-i-n junction composed of p-GaN/AlGaN/GaN in the gate stack of p-GaN HEMT, radiation-induced holes would accumulate in the channel/buffer region near the gate stack.

Based on this insight, the research team introduced a partition design with gate stacking to safely dissipate accumulated holes and improve tolerance to single particle burnout.

Their novel HEMT architecture is achieved by patterning the gate metal layer deposited on the p-GaN layer into segments, which allows some spaced metal fingers to no longer serve as gate electrodes, but to be connected to the source metal through field plate interconnect technology. Another approach different from conventional methods is to etch the p-GaN intermediate region beneath the source connecting metal, so that these metals can be directly deposited on top of the AlGaN layer to form an ohmic contact. Through this method, the source connected metal/AlGaN/GaN ohmic contact facilitates the dissipation of holes.

The electrical measurement results show that compared with the control device, the radiation resistant HEMT has higher threshold voltage and on resistance: the threshold voltage of the former is 3.3 V, while the latter is 3.0 V; The conductivity of the former is 223 m Ω, while the latter is 188 m Ω. Both of these increases are due to the buried metal structure connecting the source, which occupies a portion of the original gate region and weakens the current conduction capability.

The irradiation experiment based on heavy ion accelerator used energy transfer line densities of approximately 76 MeV cm2 mg-1 and 86 MeV cm2 mg-1, and the results showed that the average single particle burnout voltage of the radiation resistant HEMT was 558 V and 467 V, respectively. In contrast, the equivalent values of traditional HEMTs are only 217 V and 89 V, respectively.

Research has found that a 300 W power factor conversion system operating under laser irradiation achieves an efficiency of 95% at a transmission line density of approximately 76 MeV cm2 mg-1. In contrast, the efficiency of an equivalent system using radiation hardened 400 V vertical double diffusion silicon MOSFETs is only 91%.

Feng Zhou stated that the next goal is to apply radiation hardening devices to circuit systems and validate their application in aerospace electronic systems.