Accurate Measurement of Dynamic on-State Resistances of GaN Devices under Reverse and Forward Conduction in High Frequency Power Converter

Because of trapped charges in GaN transistor structure, device dynamic ON-state resistance RDSon is increased when it is operated in high frequency switched power converters, in which device is possibly operated by zero voltage switching (ZVS) to reduce its turn-ON switching losses. When GaN transistor finishes ZVS during one switching period, device has been operated under both reverse and forward conduction. Therefore its dynamic RDSon under both conduction modes needs to be carefully measured to understand device power losses. For this reason, a measurement circuit with simple structure and fast dynamic response is proposed to characterise device reverse and forward RDSon. In order to improve measurement sensitivity when device switches at high frequency, a trapezoidal current mode is proposed to measure device RDSon under almost constant current, which resolves measurement sensitivity issues caused by unavoidable measurement circuit parasitic inductance and measurement probes deskew in conventional device characterisation method by triangle current mode. Proposed measurement circuit and measurement method is then validated by first characterising a SiC-MOSFET with constant RDSon. Then, the comparison on GaN-HEMT dynamic RDSon measurement results demonstrates the improved accuracy of proposed trapezoidal current mode over conventional triangle current mode when device switches at 1MHz

State-of-the-art all-silicon sub-bandgap photodetectors at telecom and datacom wavelengths

Silicon-based technologies provide an ideal platform for the monolithic integration of photonics and microelectronics. In this context, a variety of passive and active silicon photonic devices have been developed to operate at telecom and datacom wavelengths, at which silicon has minimal optical absorption - due to its bandgap of 1.12 eV. Although in principle this transparency window limits the use of silicon for optical detection at wavelengths above 1.1 μm, in recent years tremendous advances have been made in the field of all-silicon sub-bandgap photodetectors at telecom and datacom wavelengths. By taking advantage of emerging materials and novel structures, these devices are becoming competitive with the more well-established technologies, and are opening new and intriguing perspectives. In this paper, a review of the state-of-the-art is presented. Devices based on defect-mediated absorption, two-photon absorption and the internal photoemission effect are reported, their working principles are elucidated and their performance discussed and compared

Monolithically integrated InAsSb-based nBnBn heterostructure on GaAs for infrared detection

High operating temperature i nfrared photo detectors with multi -color function that are capable of monolithic integration are of increasing importance in developing the next generation of mid -IR imag e sensors. Applications of these sensors include defense, medical diagnosis, environmental and astronomical observations. We have investigated a novel InAsSb -based nBnBn heterostructure that combines a state -of-art InAsSb nBn detector with an InAsSb/GaSb heterojuncti on detector . At room temperature, r educti on in the dark current density of more than an order of magnitude was achieved compared to previously investigated InAsSb/GaSb heterojunction dete ctors . Electrical characterization from cryogenic temperatures to roo m temperature confirmed that the nBnBn device was diffusion limited for temperature s above 150K. O ptical measurements demonstrated that the nBnBn detector was sensitive in both the SWIR and MWIR wavelength range at room temperature . The specific detectivity (D*) of the competed nBnBn devices was calculated to be 8.6 × 10 8 cm · Hz 1/2 W -1 at 300K and approximately 1.0 × 10 10 cm · Hz 1/2 W -1 when cooled down to 200K (with 0.3V reverse bias and 1550nm illumination ). In addition, all photodetector layers were grown monolithically on GaAs active layers u sing the interfacial misfit array growth mode . Our results therefore pave the way for the development of new active pixel designs for monolithically integrated mid -IR imaging arrays

On the Trade-Off Between Quality Factor and Tuning Ratio in Tunable High-Frequency Capacitors

A benchmark of tunable and switchable devices at microwave frequencies is presented on the basis of physical limitations to show their potential for reconfigurable cellular applications. Performance limitations are outlined for each given technology focusing on the quality factor (Q) and tuning ratio (eta) as figures of merit. The state of the art in terms of these figures of merit of several tunable and switchable technologies is visualized and discussed. If the performance of these criteria is not met, the application will not be feasible. The quality factor can typically be traded off for tuning ratio. The benchmark of tunable capacitor technologies shows that transistor-switched capacitors, varactor diodes, and ferroelectric varactors perform well at 2 GHz for tuning ratios below 3, with an advantage for GaAs varactor diodes. Planar microelectromechanical capacitive switches have the potential to outperform all other technologies at tuning ratios higher than 8. Capacitors based on tunable dielectrics have the highest miniaturization potential, whereas semiconductor devices benefit from the existing manufacturing infrastructure

Maximum Effectiveness of Electrostatic Energy Harvesters When Coupled to Interface Circuits

Accepted versio

Microelectromechanical Systems (MEMS) Resistive Heaters as Circuit Protection Devices

With increased opportunities for the exploitation (i.e., reverse engineering) of vulnerable electronic components and systems, circuit protection has become a critical issue. Circuit protection techniques are generally software-based and include cryptography (encryption/decryption), obfuscation of codes, and software guards. Examples of hardware-based circuit protection include protective coatings on integrated circuits, trusted foundries, and macro-sized components that self-destruct, thus destroying critical components. This paper is the first to investigate the use of microelectromechanical systems (MEMS) to provide hardware-based protection of critical electronic components to prevent reverse engineering or other exploitation attempts. Specifically, surface-micromachined polycrystalline silicon to be used as meandering resistive heaters were designed analytically and fabricated using a commercially available MEMS prototyping service (i.e., PolyMUMPs), and integrated with representative components potentially at risk for exploitation, in this case pseudomorphic high-electron mobility transistors (pHEMTs). The MEMS heaters were initiated to self-destruct, destroying a critical circuit component and thwart a reverse engineering attempt. Tests revealed reliable self-destruction of the MEMS heaters with approximately 25 V applied, resulting in either complete operational failure or severely altering the pHEMT device physics. The prevalent failure mechanism was metallurgical, in that the material on the surface of the device was changed, and the specific failure mode was the creation of a short-circuit. Another failure mode was degraded device operation due to permanently altered device physics related to either dopant diffusion or ohmic contact degradation. The results, in terms of the failure of a targeted electronic component, demonstrate the utility of using MEMS devices to protect critical components which are otherwise vulnerable to exploitation