MOVPE technology progress for GaO-based devices

High quality semi-polar (112¯2) plane AlGaN-based multiple quantum wells (MQWs) were successfully grown on (101¯0) m-plane sapphire substrates with metal-organic chemical vapor deposition (MOCVD) technology and the effects of indium (In) surfactant on the structural and optical properties of the AlGaN-based MQWs were investigated intensively. The characterization results revealed that the surface morphology as well as the crystalline quality for the semi-polar (112¯2) plane AlGaN MQWs could be improved remarkably by adopting In as surfactant during the MOCVD growth process. Furthermore, the integrated MQWs-related excition emission peak intensity and the radiative recombination probabilities in MQWs could be increased as well with the help of In-surfactant, resulting an enhanced internal quantum efficiency.

Optimization quality for indium pulse-assisted of β-Ga2O3 thin film on sapphire surface

Preparation of copper films by metal organic chemical vapor deposition on various substrates

Sintering Ag technology that shows excellent mechanical and thermal properties has become a promising solution to meet the harsh requirement of Wide Band Gap (WBG) power devices. Herein, an Ag paste contains a hybrid solvent was prepared, and its corresponding sintering profile was designed to produce robust sintered Ag joints. At a relative low temperature 150 °C, the average shear strength of sintered Ag joints can reach 49.05 MPa without pressure, which is far higher than that of traditional Sn-based solders. Robust sintered Ag joints with the highest shear strength 94.64 MPa were obtained at 230 °C. The SEM and EDS results indicate that the combining of strong internal connection and tight attachment between sintered Ag joints and substrates contributes to the high shear strength. We think the excellent results can significantly contribute to the industrial application of Ag paste in the die-attachment and realize the replacement of traditional Sn-based solders in power device packaging.

High-operating temperature MWIR nBn HgCdTe detector grown by MOCVD

Ag sinter joining which has exceptional characteristics is promising as a die-attach material for wide band-gap (WBG) power devices in electric vehicles (EVs). So far, many Ag sinter joining technologies in the range of 250 °C to 300 °C have been developed, but the industry still requires lower die-attach temperatures and more accessible processing methods. We have been pursuing technology that minimizes die-attach temperature and pressure to minimize the warpage of the power module structure. In this work, a pressureless Ag sintering was carried out in air at 175 °C without any pressure, and the bonding strength achieved approximately 37 MPa. The robust bonding mechanism of the Ag sinter joining was investigated using EBSD and XRD analysis on the microscale. This study can provide a solution for the possibility of the diebonding process at 175 °C and effective heat dissipation design of the power module.

In PV systems, the voltage of a PV panel is low and it needs to be increased to satisfy the inverter side requirements without increasing the cost by adding more PV panels. To reach this goal, a high gain DC-DC converter needs to be inserted between the PV panel and inverter. In this paper, a novel high gain boost converter is proposed to reach a high output voltage and overcome the associated drawbacks of conventional converter such as high duty ratio, and narrow turn-off interval. The proposed converter composed of interleaved structure connected to the input voltage and voltage multiplier connected to the output voltage to achieve high gain ratio. The system efficiency is improved by using wide bandgap (WBG) power devices, such as SiC MOSFET. SiC based devices have low ON state resistance, small conduction and switching losses compared to Si based devices. Simulation results show that a high output voltage of 800 V is achieved. Also, a high efficiency of 98.4% is attained at a high switching frequency of 300 kHz.

High-quality nitrogen (N)-polar gallium nitride (GaN) has great potential for fabricating high-power or high-frequency GaN-based high electron mobility transistors (HEMTs). In this article, the successful growth of the N-polar GaN films with high crystalline quality, smooth surface morphology, and low defect density on N-polar free-standing GaN substrates with metal–organic chemical vapor deposition (MOCVD) technology is reported. In particular, it was first observed that dislocations appeared in pairs on the surface of N-polar GaN films through CL images. Moreover, it was found that the size of the dislocation-dots gradually and monotonously decreased with the increase in the growth temperature but increased with the increase in the film thickness of the N-polar GaN films. These phenomena could be explained in terms of the bending, merging, and annihilation of the dislocations during the MOCVD growth process. By optimizing the growth temperature, high-crystalline-quality N-polar GaN films with a dislocation density as low as 4.30 × 105 cm–2 and a surface roughness root-mean-square value as small as 0.28 nm were achieved in this study. These results should pave a solid foundation for the subsequent research and development of high-frequency or high-power N-polar GaN-based electronic devices.

The rapid growth in renewable energy based electric power generation continuously pushes for the need of high performance power conversion systems. This paper mainly focuses on the design and performance study of a DC– DC ZETA converter using wide bandgap power devices. The converter is designed based on a SiC MOSFET/SiC Schottky diode, and its performance is compared with a Si IGBT/SiC Schottky diode based converter. The switching characteristics of the SiC MOSFET and Si IGBT power devices within the converter are studied and compared. A comprehensive evaluation of the total power loss and overall efficiency of the converter is analyzed and reported. The results indicate that the converter with the SiC MOSFET/SiC Schottky diode has great potential to work efficiently under different operating conditions.

For ferroelectric random access memory (FRAM) to be beneficial in future mobile devices, high-density FRAM with nm scaled cell should be developed. We have succeeded in scaling further the cell size of one-pass transistor and one-storage capacitor (1T1C) FRAM down to 0.27 µm2 at 150 nm technology node. Owing to new SrRuO3 (SRO) electrode technology along with ultrathin PbZrTiO3 (PZT) using metal organic chemical vapor deposition (MOCVD) technology, two-dimensional (2-D) metal–insulator–metal (MIM) ferroelectric capacitor was successfully scaled down vertically to 200 nm. By the application of a new double hard mask capacitor etching technology, 0.11-µm2-area 200-nm-thick 2-D PZT capacitor was successfully isolated with 180 nm spacing. As a result, a high remanent polarization of 40 µC/cm2 was obtained at 1.6 V on a 0.11 µm2 ferroelectric storage capacitor of the 0.27 µm2 cell 1T1C FRAM. Great advances in three-dimensional (3-D) ferroelectric capacitor, which is essential for 6–8 F2 cell 1T1C FRAM at nm scaled technology node, have been made by introducing a new atomic layer deposition (ALD) method for 3-D electrode and a novel MOCVD PZT deposition for 3-D PZT. As a result, for the first time, robust hysteresis was obtained from a 3-D PZT capacitor.

Low reverse-bias series resistance tunnel junctions (TJs) are the key to improving the performances of high efficiency multi-junction semiconductor laser diodes (MJLDs). In this paper, InGaAs QW TJ and InGaAs DQW TJ with single InGaAs layer and double InGaAs layers inserted into GaAs TJs separately, are proposed. TJ chips were fabricated by metal organic chemical vapor deposition (MOCVD) technology and semiconductor process. The measurement results of the devices display that the operating voltage of the InGaAs QW TJ and the InGaAs DQW TJ is lower than that of the GaAs TJ under the same injection current, whether it is a small current or a large current, and the InGaAs DQW TJ operating voltage is lower than that of the InGaAs QW TJ. Both GaAs TJ and InGaAs DQW TJ were applied to 1060 nm dual active region semiconductor laser diode. The ridge lasers with a strip width of 100μm and a cavity length of 2 mm were fabricated. The working voltage is reduced from 3.81 V to 3.38 V at 1 A drive current. Further experimental results indicate that the reverse-bias series resistance of InGaAs QW TJ and InGaAs DQW TJ is lower than that of GaAs TJ, and the performances of InGaAs DQW TJ are the best. This is of great significance to reduce the heat loss of MJLDs and improve its performances.

Photovoltaic (PV) energy conversion systems require fast-switching power devices that are highly efficient with low semiconductor loss under harsh environmental conditions. Silicon (Si) semiconductor devices are nearing their practical limits in meeting the ever-increasing requirements of power converters. However, wide bandgap (WBG) semiconductor devices made from silicon carbide (SiC) are exceeding these limits. SiC power devices enable more efficient and higher performance power converters. This paper presents a non-isolated dc-dc boost converter based on SiC power devices optimized for use in PV systems. The performance of two otherwise identical converters is compared, one with a new SiC MOSFET/SiC Schottky diode, and one with a conventional Si MOSFET/Si diode. A comparison of switching characteristics and energy loss of each semiconductor device is performed at different switch currents. Converter total loss and overall efficiency are evaluated at different switching frequencies, input voltages, and output power levels. The results indicate that the SiC MOSFET/SiC Schottky diode in the converter is more efficient, performs better, and has reduced power loss compared to the Si MOSFET/Si diode.

The quality enhancement of sputtering AlN has hampered a bottleneck that limits the further development and deployment of film bulk acoustic resonator (FBAR) filters. To address this bottleneck, a new two-step growth process integrating metal–organic chemical vapor deposition (MOCVD) and physical vapor deposition (PVD) technologies was carefully constructed to grow AlN films on Si substrates. It was found that both the crystallinity and the surface roughness were increased by more than double that of the one-step produced PVD AlN because of the MOCVD AlN buffer layer with smaller dislocations and grain boundaries. Afterward, using our 4-inch MEMS wafer process, high-quality AlN-based FBARs wafers were obtained accordingly with small full-width at half-maximums for two-step grown AlN(0002) X-ray rocking curves of 0.68°, showing that the Q-factor of FBARs with two-step grown AlN precedes FBARs with one-step grown PVD AlN by 57.6%.

Wide band gap semiconductors such as SiC and GaN have been expected to be established as the next generation power semiconductors, which are capable to reduce huge energy-loss in electric power conversion. The application of them will increase power density resulting in operation temperature rise beyond 200 °C. In addition, both increase of current and of frequency will also increase stress on devices. In general, power devices must possess robustness and high reliability for safe control of power conversion. Heat dissipation from the hot die in operation is one of the essential key factors for establishing high performance WBG devices. Here we report the current status of high temperature packaging materials including die-attach, wiring, substrates, molding compounds, and, in addition, reliability issues including thermal shock, power cycling and transient thermal properties.

Wide band gap semiconductors such as SiC and GaN have been expected to be established as the next generation power semiconductors, which are capable to reduce huge energy-loss in electric power conversion. The application of them will increase power density resulting in operation temperature rise beyond 200 °C. In addition, both increase of current and of frequency will also increase stress on devices. In general, power devices must possess robustness and high reliability for safe control of power conversion. Heat dissipation from the hot die in operation is one of the essential key factors for establishing high performance WBG devices. Here we report the current status of high temperature packaging materials including die-attach, wiring, substrates and molding compounds. In addition, reliability issues including thermal shock, power cycling and transient thermal properties will be summarized. A series of DBC and DBA substrates, composed of Al and Cu as metal layers and of Al2O3, AlN and Si3N4, were examined by thermal shock test between -50 °C and 250 °C. DBC substrates with Al2O3 and AlN fractured only after 10 cycles due to severe thermal stress while all DBA and DBC with Si3N4 substrates survived. Al and Cu layer of all DBC and DBA substrates severely deformed by thermal shock. By microstructural observation, grain boundary sliding during thermal shock has a key to cause deformation of metal layers on ceramics. Ni and Ni-P plating on metal layer also deformed followed by Al and Cu layer deformation. Ni-P plating showed severe cracking which can be attributed to brittleness of Ni-P plating while Ni plating did not. Ag sinter joining can be successfully applied for die attach by low temperature and low pressure bonding in air. For better bonding quality, Ag coating is the best metallization due to the specific reaction of Ag in air. By modifying solvent, Ag particles paste was modified to form a good bonding with Au surface finish. It can provide not only high temperature structural stability but also excellent thermal dissipation capability. High die-shear strength beyond 30 MPa was maintained by thermal shock between -50 °C and 250 °C up to 1000 cycles for a DBC die-attach structure. The thermal resistance of Ag sinter joined die attach is much lower than that of solder. Figure shows the example of a GaN die-attached on DBC substrate with a new Ag sinter materials at 200 °C in air without any pressure. Even on the Au metallization, the GaN die was bonded with high strength. The interface shows a good bonding between Au and Ag. This work was supported both by JST ALCA project on GaN packaging and by METI standardization project for evaluation methods of thermal properties of ceramics substrates. Figure 1