Shi Wei Ricky Lee

Background and ObjectivesExcess sugar intake in early life may affect long-term brain health, but evidence for dementia is limited. We used the abrupt end of UK sugar rationing in September 1953 as...

β-Ga₂O₃ is a competitive candidate for high-voltage power electronics because of its high critical field strength and easy access to high-quality native substrates. Rapid progress has been made in the electrical and thermal performances of β-Ga₂O₃ devices. However, the mechanical challenges presented by β-Ga₂O₃ to device packaging have hardly been addressed, specifically in the context of a press-pack package used widely in high-voltage high-capacity power devices. For the first time, this paper validates the feasibility of a β-Ga₂O₃ press-pack power device utilizing a 1200 V β-Ga₂O₃ SBD die under a quasi-uniaxial pressure of more than 20 MPa applied to a 200-μm-thick substrate. The reverse leakage current of the press-back β-Ga₂O₃ SBD remained stable under various pressures ranging from 2 MPa to 20 MPa, which indicated that no mechanical damage or defects that could have degraded the electrical performance were generated. Capacitance–voltage results showed that the Schottky barrier height was unaffected by the quasi-uniaxial pressures in the test range. Higher pressure reduced the contact resistance and the junction-to-case thermal resistance, both of which are beneficial for increasing the power capacity of the press-pack β-Ga₂O₃ SBD. Under the maximum clamping pressure of 20 MPa, the steady-state junction temperature rise did not exceed 150 K at DC 10 A and a corresponding heating power of over 27 W, from which a junction-to-case thermal resistance of below 5 K/W was determined.

We present a GaN-HEMT/SiC-JFET cascode device that replaces the most performance-and reliability-limiting low-mobility MOS channel of SiC MOSFETs with a high-quality GaN 2-D-electron-gas (2DEG) channel. Compared with SiC MOSFETs, the p-GaN gate-stack of the GaN/SiC cascode device delivers much lower gate charge Q_G, thermally stable threshold voltage V_TH, smaller specific ON-resistance R_ON.SP, and faster switching speed with substantially lower switching loss. A compact 3-D co-packaging solution with stacked GaN and SiC chips results in greatly reduced parasitic interconnection inductance (L_P), thereby suppressing the switching delay and switching loss. More importantly, the ultralow L_P is shown to play a critical role in reclaiming the dv/dt controllability, which has long been a prevalent issue for cascode devices that make them vulnerable to electromagnetic interference (EMI) issues. With an ultralow L_P, an increased capacitive gate-to-drain coupling (i.e., C_GD) in the low-voltage gate control GaN HEMT would allow strong dv/dt control via changing the external gate resistance R_G in the gate driver circuit, which is the most simple and user-friendly control method in applications. The demonstrated GaN/SiC cascode device unveils an ultimate power device that unlocks the full potential of wide bandgap (WBG) semiconductors.

A professional closet with highly efficient disinfection for reusing protective clothing is required to reduce supply and demand and protect the environment. A self-developed ultraviolet-C (UVC) light-emitting diode (LED) package that can emit uniform radiance in a certain distance was developed; and a series of disinfection modules with UVC LED packages were installed in a closet for disinfection. A disinfection module can achieve an over 99.9% disinfection rate of H1N1; E. coli; S. aureus; Pseudomonas aeruginosa; and an over 99% disinfection rate of EV71 within a minute. A 1-min disinfection closet was developed to reuse protective clothing. The closet was well-designed; as well as a series of burn-in tests were performed after the assembly of the closet. The optical and thermal properties of the closet were stable within one minute of a working period during the burn-in test. After disinfection; bacterial filtration efficiency (BFE) and viral filtration efficiency (VFE) were examined on the disposable protective clothing. The disposable protective clothing did not show any degradation after being exposed to UVC for sixty minutes; which means the defensive capability of medical protective clothing can be reused sixty times in light of the self-developed disinfection closet. The disinfection closet provides an efficient method for reusing protective clothing.

This study presents an innovative packaging scheme for an implantable medical device which is an episcleral surface stimulator applying trans-scleral electrical stimulation. The stimulator employs an application-specific integrated circuit to facilitate wireless connection and electrical stimulation. The proposed packaging scheme considers the safety, functionality, reliability, and particularly manufacturability of the stimulator. The packaging process is structured into chip-level, component-level, and device-level. At the initial chip-level packaging, a silicon interposer is introduced to enhance the manufacturability and increase the bonding strength. At the component-level packaging, a flexible printed circuit (FPC) integrates all the components to enable the electrical functions. The FPC is curved by the bending method. The specialized design of the stack and layout addresses the biocompatibility concern. Finally, the device-level packaging incorporates Parylene-C coating and silicone encapsulation to form the final stimulator. At this packaging stage, a novel strategy is introduced eliminating the challenging Parylene-C etching process while streamlining the bending and the silicone encapsulation processes. The outstanding manufacturability achieved from the proposed packaging scheme allows consistent product quality, leading to trustable reliability validation. The reliability of the stimulator is approved by a high-temperature saline soaking test which indicates a minimum 6.1-year lifespan. Additionally, trial surgeries on a rabbit validate the shape and softness, and the biocompatibility of the stimulator is also confirmed by implantation tests on mice.

The effectiveness of ultraviolet-C light-emitting diodes (UVC LEDs) is currently limited by the lack of suitable encapsulation materials, restricting their use in sterilization, communication, and in vivo cancer tumor inhibition. This study evaluates various silicone oils for UVC LED encapsulation. A material aging experiment was conducted on CF1040 (octamethylcyclotetrasiloxane), HF2020 (methyl hydro polysiloxanes), and MF2020-1000 (polydimethylsiloxane) under UVC radiation for 1000 h. The analysis assessed transmittance changes and chemical composition alterations throughout the aging process. Notably, HF2020 showed an increase in transmittance before 500 h, indicating a curing process attributed to the photolysis of Si-H, leading to the formation of Si-O-Si. Further testing on 265 nm UVC LEDs, both with and without HF2020 encapsulation, showed that the encapsulated LEDs exhibited a remarkable maximum increase of 27% in radiant power compared to their unencapsulated counterparts. Additionally, these encapsulated LEDs sustained higher radiant power levels during the first 200 h of operation. Notably, its potential application in photodynamic therapy is significant; by activating photosensitizers with higher UVC exposure, it facilitates the rapid production of reactive oxygen species, leading to effective cancer cell destruction within a short timeframe.

To unlock the full fast-switching potential of the GaN-HEMT/SiC-JFET cascode device, parasitic interconnection inductances are minimized with a 3-D stacked co-packaging configuration. This configuration offers the benefits of reduced switching loss and suppressed oscillation. Equipped with the 3-D co-package configuration, the dv/dt control capability of the GaN/SiC cascode device is enhanced by introducing an additional gate-drain capacitor, C_GD-LV, to the low-voltage GaN HEMT. This additional C_GD-LV improves the coupling between the input control gate voltage and the JFET's gate voltage, which ultimately determines the switching speed of the GaN/SiC cascode device. Experimental results verified the GaN/SiC cascode device, when equipped with the 3-D co-packaged configuration and the additional C_GD-LV, demonstrated fast switching capability with adequate dv/dt control.

Background: More effective and automated techniques for disinfecting elevator push-buttons currently need to be developed, especially given that they are frequently touched by hundreds of individuals. Methods: An automatic elevator push-button disinfection device equipped with four 265 nm ultraviolet-C (UVC) light-emitting diode (LED) packages has been developed for disinfection after each touch to reduce the risk of infection. In this paper, the UVC leakage test, UVC LED package reliability test, and bacteria disinfection efficiency test were performed. Results: The disinfection efficiency for Staphylococcus aureus and Escherichia coli can reach over 90% in 10 s, and end users can set multiple disinfection periods in light of their circumstances. The disinfection device is safe for the human body if the distance exceeds 120 mm. The accelerated aging test result demonstrates that the disinfection device is reliable under normal operation and end-users can increase the disinfection time by compensating for the irradiance drop. Conclusions: The automatic elevator push-button disinfection device provides a safe, highly efficient, and stable disinfection solution for elevator push-buttons.

Process monitoring is a valuable tool in the modern injection molding industry for assessing process health, maintaining safety, and improving product quality. However, to truly tap into the potential of process monitoring, new advancements in sensing technology must be made. Currently, the industry only has a way to monitor the cavity conditions (temperature and pressure) where the product is formed, lacking an online method to monitor in-mold material behaviors. This gap can be bridged by the innovative use of a capacitance sensor, which allows for the real-time characterization of the in-mold material’s dielectric properties and monitoring its status during the molding process. In this work, we develop a low-cost, highly integrated, compact sensing probe capable of simultaneously measuring pressure, temperature, and capacitance signals at the same location, providing comprehensive data for analysis. The sensor is designed, fabricated, and validated through real injection molding experiments. The analysis shows that the capacitance signal can monitor the in-mold material status throughout the cycle, with its endpoint signal strongly correlated with product shrinkage. Furthermore, excellent part weight and thickness prediction results using the machine learning models demonstrate the effectiveness of the sensor signals for injection molding quality monitoring.