【Member Papers】Xidian University Haoyue&Han Genquan Team —— Highly Stable Electronics Based on β-Ga₂O₃ for Advanced Memory Applications

      Researchers from the Xidian University have published a dissertation titled "Highly Stable Electronics Based on β-Ga₂O₃ for Advanced Memory Applications" in Advanced Science.

Program Support

      The authors acknowledge support from the China Postdoctoral Science Foundation (2023M742732), thePostdoctoral Fellowship Program of CPSF under Grant Number GZC20241303, theFundamental Research Funds for the Central Universities (XJSJ24100), the National Natural Science Foundation of China (Grant No. 62404176, 62025402, 62090033, 92364204, 9226420, 12175298, and 62293522)and the Major Program of Zhejiang Natural Science Foundation (Grant No. LDT23F04024F04). The authors thank beamlines BL17B1, BL16U1, BL06B, BL19U2, BL02U2, and BL01B1 staff at the SSRF and User Experiment Assist System of SSRF for their help. The authors thank Professor Chang-Tai Xia's group from the Key Laboratory of Materials for High Power Laser Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences for providing the β-Ga₂O₃ single crystal bulk. And Chang-Tai Xia acknowledges the National Natural Science Foundation of China (No. 51972319) and the Science and Technology Commission of Shanghai Municipality (No. 19520744400).

Abstract

      Wide-bandgap (WBG) semiconductors are at the forefront of driving innovations in electronic technology, perpetuating Moore's Law and opening up new avenues for electronic devices. Although β-Ga₂O₃ has attracted extensive research interest in advanced electronics, its high-temperature and high-speed volatile memory applications in harsh environment has been largely overlooked. Herein, a high-performance hexagonal boron nitride (h-BN)/β-Ga₂O₃ heterostructure junction field-effect transistor (HJFET) is fabricated, exhibiting an off-state current as low as ≈10 fA, a high on/off current ratio of ≈10⁸, a low contact resistance of 5.6 Ω·mm, and an impressive field-effect electron mobility of 156 cm² （Vs）⁻¹. Notably, the current h-BN/β-Ga₂O₃ HJFET exhibits outstanding thermal reliability in the ultra-wide temperature range from 223 to 573 K, as well as long-term environmental stability in air, which confirms its inherent capability of operation in harsh environments. Moreover, the h-BN/β-Ga₂O₃ HJFET demonstrates successful applications for accelerator-in-memory computing fields, including dynamic random-access memory structure and neural network computations. These superior characteristics position β-Ga₂O₃-based electronics as highly promising for applications in extreme environments, with particular relevance to the automotive, aerospace, and sensor sectors.

Experimental Section

Device Fabrication

      In this work, the β-Ga₂O₃ bulk single crystal with 0.05 mol % Ta doping was used. It exhibits an active electron concentration of 1.4 × 10¹⁸ cm⁻³ measured by Hall effect and electrical resistivity tests. Subsequently, β-Ga₂O₃ flakes were exfoliated mechanically from β-Ga₂O₃ bulk by commercial Scotch tape and transferred onto 110 nm SiO₂/p⁺⁺-Si substrate. Then, the electron-beam lithography (EBL) process was used to pattern the source/drain regions, followed by the development, e-beam evaporation, and lift-off processes. The stack metal of Ti/Al/Ni/Au (20/100/60/80 nm) was chosen to use as a source/drain electrode. And an RTA process in a high purity N₂ ambient was also carried out at 470 °C for 1 min to improve electrode/channel contact. After the fabrication of a two-terminal β-Ga₂O₃ device, the mechanically exfoliated h-BN flake was precisely transferred to the top of the target β-Ga₂O₃ channel as the gate dielectric layer using a poly (dimethylsiloxane) transfer method. Finally, the top gate composed of Ti/Au (10/70 nm) was defined via a second EBL, metallization, and lift-off processes to finish the fabrication of h-BN/β-Ga₂O₃ HJFET.

Microscopic and Electrical Characterizations

      The crystalline structure of β-Ga₂O₃ bulk single crystal was obtained by the Synchrotron-based GIXRD which uses X-ray with a wavelength of 0.6887 Å. The Raman spectrum was investigated using a commercial Raman spectrometer (Horiba Jobin Yvon LabRAM HR800) equipped with an excitation wavelength of 532 nm. The β-Ga₂O₃ flakes structural analysis was analyzed using HR-TEM (Talos F200X). The thicknesses of h-BN and β-Ga₂O₃ flakes were determined via AFM (Bruker Dimension Icon). The all-electrical measurements were conducted by using a semiconductor analyzer (Agilent B1500A).

Summary

      In summary, a h-BN/β-Ga₂O₃ HJFET has been fabricated with a low I_off of ≈10 fA, a high I_on/I_off of ≈10⁸, a low R_c of 5.6 Ω·mm, and a high μ_fe of 156 cm² (Vs)⁻¹. Importantly, the obtained h-BN/β-Ga₂O₃ HJFET shows not only good thermal reliability in a temperature range of 223–573 K but also high environmental stability even after 18 months. Besides, the h-BN/β-Ga₂O₃ HJFET can also be used successfully in accelerator-in-memory computing fields including DRAM and neural network computation applications. This work provides a new perspective for the development of next-generation nanoelectronics.

Graphic Abstract