ε‐Ga₂O₃: An Emerging Wide Bandgap Piezoelectric Semiconductor for Application in Radio Frequency Resonators

Abstract

The explosion of mobile data from the internet of things (IoT) is leading to the emergence of 5G technology with dramatic frequency band expansion and efficient band allocations. Along with this, the demand for high-performance filters for 5G radio frequency (RF) front-ends keeps growing. The most popular 5G filters are constructed by piezoelectric resonators based on AlN semiconductor. However, AlN possesses a piezoelectric constant d 33 lower than 5 pm V −1 and it becomes necessary to develop novel semiconductors with larger piezoelectric constant. In this work, it is shown that strong piezoelectricity exists in 𝝐-Ga 2 O 3 . High-quality phase-pure 𝝐-Ga 2 O 3 thin films with a relatively low residual stress are prepared. A switching spectroscopy piezoelectric force microscope (SS-PFM) measurement is carried out and the piezoelectric constant d 33 of 𝝐-Ga 2 O 3 is determined to be ≈10.8-11.2 pm V −1 , which is twice as large as that of AlN. For the first time, surface acoustic wave (SAW) resonators are demonstrated on the 𝝐-Ga 2 O 3 thin films and different vibration modes resonating in the GHz range are observed. The results suggest that 𝝐-Ga 2 O 3 is a great material candidate for application in piezoelectric devices, thanks to its wide bandgap, strong piezoelectric property, small acoustic impedance, and low residual stress.

Electrical and Recombination Properties of Polar Orthorhombic κ-Ga2O3 Films Prepared by Halide Vapor Phase Epitaxy

“…In our earlier work [ 30 ], we reported the experimental observation of a 2DHG at the heterointerface of κ-Ga 2 O 3 films with basal plane (0001) AlN on Si(111). It has also been suggested that the considerable piezo-electric polarization of κ-Ga 2 O 3 could be employed in RF resonators and modulators [ 31 ].…”

β-Ga2O3: ultralow-loss and low-permittivity dielectric ceramic for high-frequency packaging substrate

“…Ga 2 O 3 is thus considered a new-generation semiconductor that meets the power demands of semiconductor devices and integrated technologies towards higher energy efficiency, higher voltage-resistance and higher frequency. 5,6 Meanwhile, Ga 2 O 3 exhibits numerous potential applications in terms of high-power semiconductor devices, light-emitting diode chips, and various sensor components. 7,8 As advanced packaging technologies, multi-chip modules (MCM) and a system-in-a-package (SiP) can provide excellent "More-Than-Moore" solutions.…”

Bandgap Engineering and Oxygen Vacancy Defect Electroactivity Inhibition in Highly Crystalline N-Alloyed Ga2O3 Films through Plasma-Enhanced Technology

“…In contrast to third-generation semiconductors, such as GaN and SiC, β-Ga 2 O 3 possesses several advantages, including a wider bandgap, a higher breakdown field strength, and the ability to easily grow high-quality single crystals in large sizes. − As a result, β-Ga 2 O 3 -based photodetectors have demonstrated exceptional sensitivity and responsivity in the deep-ultraviolet (DUV) range, making them ideal for DUV sensing and imaging applications . Moreover, β-Ga 2 O 3 -based transistors have exhibited remarkable electron mobility, which makes them highly suitable for high-frequency and high-power electronic applications. − However, during the growth process, Ga 2 O 3 inevitably introduces oxygen vacancies, which pose significant challenges to intrinsic carrier regulation, − p-type doping, − and the formation of stable Schottky contacts. , For instance, the presence of oxygen vacancies leads to persistent photoconductivity (PPC) effects, resulting in unexpected photoconductive gains but slow response speed due to trapping effects. − Furthermore, the oxygen vacancy defects (V O ) on the surface of Ga 2 O 3 cause electrons to be transported through tunneling puncture effects that result in the high reverse leakage current of transistors. − …”