AlScN films are produced in a commercial metal–organic chemical vapor deposition (MOCVD) system modified to low‐vapor‐pressure Sc metal–organic precursors. Growth conditions are optimized for surface morphology, film stress, and piezoelectric coefficient across a range of compositions. Epitaxial structures are designed to eliminate internal tensile stresses that develop during the film growth as well as prevent surface adatom interactions unique to the MOCVD process. From these films, wide‐bandwidth resonators and filters are manufactured using a novel microelectromechanical‐based bulk acoustic wave (BAW) transfer process. When tested on‐wafer, resonators exhibit a of 10.5%, and a value of 1400. Ladder‐type RF filters using these resonators are fabricated at 6.2 GHz and show improved performance over filters fabricated using physical vapor deposition‐deposited AlScN.

We report XBAW, a bulk acoustic wave (BAW) manufacturing technology using a unique transferred substrate process for next generation 5G and Wi-Fi 6/6E/7 application. This work reports performance metrics of resonators and filters built from high quality Aluminum Scandium Nitride (AlScN) piezoelectric films of varying Sc concentrations grown on 150mm < 100 > silicon substrates. Bulk acoustic wave resonators were fabricated using XBAW technology ranging from 5 GHz to 7 GHz and using varying Sc concentrations. The trade space between acoustic Q factors and $\text{k}_{t}^{2}$ and dependence on Sc concentration is presented. We report multiple distinct filtering solutions for WiFi 6/6E/7 systems enabling optimal and flexible system utilization of available 160 MHz channels in UNII bands 1 through 8, including a diplexer with 50 dB of isolation between channels. These results show XBAW capability to extract maximum resonator FOM from AlScN, enabling optimal design of high-performance filters.

Wi-Fi 6/6E uses 160 MHz channels in UNII-5/6/7/8 bands in 5-7GHz spectrum for maximizing data rates. A critical challenge for Wi-Fi 6E RF filters is low insertion loss in the 160MHz UNII-5 transmit band while adequately rejecting UNII bands 1, 2C, 3 & 4, which end only 50MHz below the first channel of the UNII-5 band. A 160MHz Wi-Fi 6E bulk acoustic wave (BAW) filter with UNII-5 average pass band insertion loss better than 2dB and 60dB rejection in the UNII-4 band is reported. A unique BAW device fabrication process capable of utilizing a wide variety of piezoelectric thin films is used to manufacture this challenging filter. Fabricated resonators show a maximum quality factor of 2500.

The authors report a Bulk Acoustic Wave (BAW) filter technology built using a 6-inch MEMS wafer process on a Si substrate, compatible with single crystal and polycrystalline aluminum nitride (AIN) piezoelectric materials (denoted as XBAW), and present metrics demonstrating resonator technology capable of highly reliable, high power, compact, high performance RF filter solutions in the sub-6 GHz spectrum, with proven high Qmax of 3685 and resonator Figure-Of-Merit (FOM) of 222 at 1.8GHz. Using the XBAW process, the authors compare power handling capability of filters built from single crystal Metal-Organic Chemical Vapor Deposition (MOCVD) AIN and polycrystalline Physical Vapor Deposition (PVD) AIN piezoelectric materials, showing that power handling capability of single crystal MOCVD AIN XBAW technology exceeds PVD AIN XBAW by 2.3x, when packaged and by 1.8x, when measured on-wafer. A first reliability study shows that survival times of single crystal MOCVD AIN XBAW filters far exceed survival times of PVD-AIN XBAW filters. As an example of high frequency capability, the authors report filters with a center frequency of 5.25 GHz, a 3dB bandwidth of 205 MHz, a minimum insertion loss of 0.83dB, excellent wide band rejection from 30 MHz to 11 GHz and attenuation greater than 50dB in the UNII 2C+3 bands.

5.24GHz bulk acoustic wave filters, utilizing undoped single crystal aluminum nitride, are reported. The filters had an absolute 4dB bandwidth of 151 MHz, a minimum insertion loss of 2.82 dB and rejection >38 dB. Resonators show k 2 eff of 6.32%, Q rnax of 1523, and FOM of 96.

Bulk acoustic wave (BAW) filters operating at center frequency of 3.7GHz, comprising of BAW resonators utilizing single crystal aluminum nitride (AlN) piezoelectric films epitaxially grown on silicon carbide (SiC) substrates, are reported. Metal-organic chemical vapor deposition (MOCVD) growth was used to obtain single crystal AlN films on 150-mm diameter c-plane semi-insulating SiC substrates with (0004) X-ray diffraction (XRD) rocking curve full-width half-maximum (FWHM) of 0.025°. The fabricated filters (1.25×0.9 sq.mm) had a center frequency of 3.71GHz and a 3dB bandwidth of 100MHz, an insertion loss of 2.0dB and narrow band rejection of 40dB and out-of-band rejection in excess of 37dB to 8GHz. Individual resonators on the same wafer show an electro-mechanical coupling as high as 7.63% and maximum quality-factors up to 1572. Insertion loss of 5ohm resonators configured as individual 2-port devices changed by 0.15dB after high power survival test at 10W. This is the first demonstration of single crystal AlN-on-SiC based BAW resonator and filter technology at 3.7GHz and illustrates the potential of a single crystal AlN-on-SiC based BAW technology platform enabling compact, high power and high performance filter solutions for high frequency mobile, Wi-Fi and infrastructure applications.

In recent years, film bulk acoustic resonators (FBARs) have become important in the mobile handset market for their small size compared to surface acoustic wave resonators, their compatibility with existing integrated circuit processes, and their usage in synthesizing components such as filters and duplexers. In this work, we demonstrate through finite element simulation using COMSOL MultiPhysics and experimental data, that single crystal FBARs outperform current polycrystalline devices with their higher mechanical coupling efficiency and quality factor. We also present elasticity coefficients extracted from experimental data on fabricated devices.

Bulk acoustic wave (BAW) resonators using single crystal AlGaN piezoelectric films are reported. Metal-organic chemical vapor deposition (MOCVD) growth was used to obtain single crystal AlGaN films on 150-mm diameter <111> silicon substrates with (0002) XRD rocking curve FWHM of 0.37°. Series-configured 12 Ω BAW resonators with resonant frequency of 2.302GHz were fabricated with insertion loss of 0.29dB and an electromechanical coupling of 4.44%. Maximum resonator Q max was 1277, leading to a figure of merit (FOM) of 57. Unloaded acoustic Q r was 4243, leading to a FOM of 188. These FOM are the highest reported to date for MOCVD-based single crystal resonators.

The purpose of this work was to investigate the validity of Arrhenius accelerated-life testing when applied to gallium nitride (GaN) high electron mobility transistors (HEMT) lifetime assessments, where the standard assumption is that only critical stressor is temperature, which is derived from operating power, device channel-case, thermal resistance, and baseplate temperature. We found that power or temperature alone could not explain difference in observed degradation, and that accelerated life tests employed by industry can benefit by considering the impact of accelerating factors besides temperature. Specifically, we found that the voltage used to reach a desired power dissipation is important, and also that temperature acceleration alone or voltage alone (without much power dissipation) is insufficient to assess lifetime at operating conditions.

The authors report on an electrical and optical analysis of AlGaN/GaN HEMTs stressed under high electric field conditions into a state of permanent degradation, evidenced by an increase in OFF-state leakage current and a reduction in breakdown voltage. A method of stress testing AlGaN/GaN HEMTs to voltages close to breakdown while protecting the device from catastrophic failure is presented. Using this stress method, a detailed study was performed to observe device degradation that limits safe operation in the OFF-state. Electrical analysis reveals that quantitatively the Schottky properties of the gate diode are degraded by the stress and suggests a localized defect. An optical analysis confirms localized degradation via electroluminescence (EL) spots on the stressed side of the gate finger. It is shown that the dominant EL site in the degraded device may be observed prior to the application of stress. Finally, it is confirmed that the localized EL emission of the stressed device is the dominant gate leakage path via thermal imaging. These results suggest a method for identifying and understanding the failure mechanisms that limit the safe operating area of GaN HEMTs.

In the early 1990s, gallium nitride (GaN) was deemed an excellent, next generation, semiconductor material for high power/high frequency transistors based on the material parameters of bandgap, electron mobility, and saturated electron velocity. The lack of bulk GaN source material led to the need for GaN growth on mismatched substrates such as Si, SiC and sapphire, but fundamental material develo...

The authors report on the fundamental failure mechanisms limiting maximum applied voltage in AlGaN/GaN HEMTs. Device failure in high voltage off state conditions was studied by controlling drain leakage current and maximum applied drain voltage simultaneously. It was found that failure was associated with loss in gate control of channel current and a permanent degradation of gate diode leakage current. No permanent significant change until device failure was observed in ON-state parameters such as Ron, Idss and Idmax, thus distinguishing this failure mode from the inverse pieozo-electric effect as reported in literature.

We performed an experiment on AlGaN/GaN HEMTs with high voltage and high power as stressors. We found that devices tested under high power generally degraded more than those tested under high voltage. In particular, the high-voltage-tested devices did not degrade significantly as suggested by some papers in the literature. The same papers in the literature also suggest that high voltages cause cracks and pits. However, the high-voltage-tested devices in this study do not exhibit cracks or pits in TEM images, while the high-power-tested devices exhibit pits.

High-voltage AlGaN/GaN HFETs can produce high RF output power with nearly ideal power-added efficiency. But widespread adoption of these HFETs has been limited by a lack of acceptable reliability data for practical communications and radar applications. Device problems that have been observed include dc current and RF output power degradation as a function of time when the device is operating. Sudden and permanent degradation shifts in device performance have also been observed under certain operating conditions. Identified causes of the reliability problems include the quantum mechanical tunneling of electrons on the gate electrode to the surface of the semiconductor adjacent to the gate on the drain side, and a defect generation mechanism that occurs at a high, critical electric field. The gate leakage phenomenon described in this article produces electrons on the surface of the AlGaN layer adjacent to the gate electrode, and this creates a negative charge layer that partially depletes the conducting channel, thereby producing a degradation in dc current and RF output power. The gate leakage current is present when the device is biased and driven with an RF signal, and therefore the charge accumulation increases as a function of operation time. The gate tunnel current is a very sensitive function of surface state density, particularly near the gate edge, and of the magnitude of the electric field at this location. In addition, at a critical magnitude of the electric field defects in the AlGaN layer are created due to mechanical stress on the crystal structure, and these defects act as charge trapping centers. This mechanism is not well understood at this time and is currently the subject of research and investigation. Parameters that affect reliability are a function of device design and surface processing. Improvements in device reliability have been achieved through design modifications to produce improved surface passivation layers that reduce the gate and surface leakage currents and further modifications to reduce the magnitude of the electric field internal to the device. Continuing reliability study is required to fully elucidate the link between observed degradation behavior and physical failure mechanisms in a statistically significant manner.

GaN HEMT reliability evaluation in a typical Arrhenius manner requires establishing peak junction temperature for a particular stress condition. Several new techniques have yielded promising results toward establishing peak temperature for these devices in combination with detailed physical modeling, particularly micro-Raman imaging. This paper compares results from finite element modeling to measurements by, infrared imaging and micro-Raman imaging. The limitations of IR imaging were confirmed similar to earlierreports. Two techniques for establishing temperature from micro-Raman measurements were used to reveal excellent correlation to the model, and also provide insight into the relationship between temperature and structural change in the, device. Temperature modeling data is reported for base plate temperature from 85 degrees C to 250 degrees C for practical GaN HEMT devices. Implications of the measurements for GaN HEMT reliability stress testing and analysis will be disscussed.