Research Area

Due to the explosive growth of low-power portable wireless 5G (3.5-6 GHz and 24-86 GHz) technology in the smart cities, there is a great interest in developing micro-scaled high-frequency sensors and energy harvesters for generating useful dc power using ambient radiofrequency (RF) and mm wave energy. Furthermore, many global cities are further expanding toward the future prospectus of 6G (95 GHz and above) and mm Wave (30-300 GHz) technologies for much faster (targeting 1Tb/s) and secured data transmission. This enables the critical need for the development of compact, highly sensitive broadband high-frequency rectifiers to be used in the next-generation sensor technologies.

The wide-range application of these high-frequency rectifiers are proposed in the fields of biomedical, telecommunication, meteorology, radars, etc. The energy harvesters of electromagnetic field in the microwave to mm wave frequency range (few GHz to 300 GHz) are in great demand. The concept of energy harvesting becomes essentially useful for the high-shelf life and self-sustainability of the next-generation sensors (such as temperature, humidity sensors) placed in the smart cities, which can be integrated with high-frequency rectifiers for the wireless charging from the ambient EM waves to reduces/removes the dependency on the battery.

The focus of our group is to develop the efficient high-frequency rectifiers based on the quantum properties of topological materials (TMs) like Dirac/Weyl semimetals and topological insulators and spin rectification effect in ferrimagnet due to the interplay of time varying resistance and ac signal, that can address the challenges faced by the current semiconductor diodes, with the final aim of integrating and scaling them in the commercial energy harvesting system operating at microwave to mm wave frequencies.

Existing high-frequency rectifiers and energy harvesters are mainly based on semiconductor diodes, which suffers from the thermal threshold voltage, limited transit time, and are limited to low frequencies, high junction-area and high impedance. Furthermore, there is a so-called terahertz gap (0.1 to 10 THz) between the operating frequencies of electrical diodes and photodiodes. At frequencies within this range, the efficient detection technology remains to be developed. Instead of using semiconductor junctions, rectification can be realized as the nonlinear electrical or optical response of non-centrosymmetric topological materials or resonant ferrimagnetic materials. Rectification in a single homogenous material is not limited by the thermal voltage threshold. Second-order nonlinearity can be utilized in applications requiring frequency doubling or rectification such as energy harvesting, wireless communications and IR detectors. Nonlinear Hall effect (NLHE) is an example of such quantum property of the material, which can be used for energy harvesting purposes. Topological materials with strong Berry curvature and extrinsic effects are expected to show wide-frequency-range rectification. On the other hand, ferrimagntic/non-magnetic materials has shown a high-frequency response due to exchange modes of sub-lattices excited by the spin current from heavy metal layer. Beside developing rectifiers, our group plan is to use the spin-orbit coupling (SOC) phenomena to develop Spin-Hall nano-oscillators (SHNOs) in the GHz and sub-THz regime.