The theme of our research is to design, fabricate, characterize, and model electronic devices (diodes, transistors, sensors, supercapacitors, drug delivery devices etc.) around electronic materials (III-V compound semiconductors, nitride semiconductors, perovskites, dielectrics, graphene, polymers etc.) for various applications including high frequency electronics, high power electronics, energy storage, biosensors, gene/drug delivery, and neuromorphic computing, . The following is a synopsis of our current research.
High Composition AlGaN Based High Power Density mm-Wave Electronics
Superior material properties of AlGaN make it a promising candidate as a channel material for high power mm-wave transistors due to its large bandgap and high breakdown field. Also, previous research has suggested that the saturation velocity vsat of AlGaN alloys is comparable to GaN. With a higher breakdown field and similar saturation velocity, the Johnson’s figure of merit of AlGaN channel transistors is higher than GaN channel transistors, which means it can deliver more RF power at high frequencies. We’ve achieved 40 GHz fT on 60% AlGaN channel with MBE regrown contacts and 2.7 W/mm Pout on 40% AlGaN channel with micro-channel design (FinFETs).
Perovskite Oxide Based High Power Density mm-Wave Electronics
Perovskite oxide BaSnO3 features a high room temperature mobility with high sheet charge concentration. The high-k dielectric feature of the gate dielectric enables phenomenal device performance (field management improvement). We investigate on the heterostrured field effect transistors performance of BaTiO3/BaSnO3 featuring high output current and transconductance. ICP-RIE etching characterizations have been performed on the epitaxial grown films of BaSnO3 and BaTiO3 using BCl3/Ar.
GaN PN diodes
Vertical GaN pn diodes based on bulk GaN substrates are in high demand due to their potential for high performance and efficiency owing to the large bandgap and high breakdown electric field. Using simple mesa isolating structures and optimized ohmic contacts we can fabricate devices that reach their fundamental material limits. The devices go through a number of DC measurements such as CV, Forward Bias and Reverse Bias that reveal critical information about the devices. The ideality factor of the device is approximately 1.15 and turn-on resistance is close to 0.47 mOhm-cm2. The breakdown voltage of the device goes as high as 1028 V. Even without any kind of passivation or edge termination these devices perform better than a lot of the similar structured benchmark devices
Thermal Management of Wide-bandgap Semiconductor Devices
Power electronics has been an integral part of any power systems and high-power wide bandgap (WBG) devices are very attractive owing to its high switching frequency and high efficiency. As the power consumption increases in electronic devices, the excess heat presents a threat to reliability and can lead to premature failure. Understanding and finding ways to improve the device performance and reliability is critical in health management of such power systems. CVD -grown graphene and Vacuum annealed graphene were both reliable to overcome this challenge. Following the package design and heat spreader deposition was tackled, finally leading into test the performance degradation and reliability of the devices under stress.
A Field-effect transistor-based biosensor or “BioFET” is a field-effect transistor where the device current is modulated by the binding of biological molecules to the gate region. BioFETs can be functionalized with variable receptor elements to sense a wide array of biological analytes, such as proteins, bacteria, and toxins. AlGaN/GaN heterostructures provide a biocompatible, robust, and chemically inert sensing platform. In addition, they can provide high sensitivity compared to many other sensing approaches. The detection of DNA hybridization, cyanobacterial toxins, and protein binding has been performed using both recessed and non-recessed AlGaN/GaN biosensors in the lab.
Cell Electroporation with nanolithography
Electroporation is a technique where an external electric field is applied to a target cell population with the purpose of increasing membrane permeability, allowing for the introduction of foreign material into the cells. This foreign material may include various chemicals, drugs, or DNA, which is generally intended to modify the cell population so that it exhibits a desired behavior. While other intracellular delivery methodologies exist, such as micro-injection and sonoporation, electroporation is often favored among these methods, due to its user-friendliness and lack of manual manipulation. Using standard silicon fabrication techniques, a 3D micro- or nano-electroporation system can be realized, possessing both the high cell viability and dose control of 2D nano-electroporation as well as the high throughput of conventional or “bulk” electroporation.