Rectennas for Thermal-Energy Conversion

We demonstrated the conversion of thermal energy in the form of far- and mid-infrared using a micro rectenna, consisting of a spiral antenna coupled to an ultra-fast nanodiode, the so-called self-switching device (SSD). A maximum efficiency of 0.02 % was measured at a 973 K (700 °C) using a calibrated black-body radiator illuminating the rectenna. The relatively low efficiency was due to the impedance mismatch between the diode and the antenna, and can be reduced by designing a suitable matching structure. The fabrication of larger rectenna array could be exploited, for example, to harvest wasted thermal energy from exhaust pipes and industrial machinery

High-Performance Atomic Layer Deposited Al2O3 Insulator Based Metal-Insulator-Metal Diode

The fabrication of metal–insulator– metal (MIM) diode using an ultrathin Al2O3 insulator layer, deposited using atomic layer deposition (ALD) is presented. The Al2O3 insulating layer was found to be highly uniform throughout the diode junction, effectively overcoming the main fabrication challenge in MIM diodes. The diodes exhibit strong non-linear current–voltage curves, have a typical zero-bias curvature coefficient of 5.4 V−1 and a zero-bias resistance of approximately 118 kΩ, a value considerably smaller than other MIM diode topologies and that allows more current to be rectified. Other results including current ratio and yield of the diode also competes favorably with the state-of-the-art MIM diodes such as the recently produced metal-octadecyltrichlorosilane (OTS)-metal structure

THz Imaging with Broadband Thermal Sources

We developed a THz imaging system based on a broadband thermal source (at 500°C) and an asymmetric semiconductor nanochannel, the self-switching nanodiode (SSD), as a room-temperature detector. The maximum resolution was better than 0.5 mm full width at half maximum. The radiation was coupled to the SSD through a microantenna, whose geometry determined the frequency bandwidth of the system. While not as accurate as coherent imaging, the compactness, low-cost, and flexibility make this system attractive for a large range of applications in medical imaging and industrial quality control

Tilting micromirror platform based on liquid dielectrophoresis

This study presents an electrically actuated tilting micro platform based on liquid dielectrophoresis with three axes movement using three droplets situated 120° apart from each other. The interdigitated electrodes produce a non-uniform electric field that generates a body force. The dielectrophoretic mechanism is responsive within at least 30 ms, and it eliminates the solid-solid contact. The tilting platform enabled an angular coverage up to 0.9° (±0.02°), with a maximum displacement of 120 µm. The tilting micromirror platform has beam steering characteristics suitable for various optical applications. The actuating platform sensor is a cost-effective and simple alternative method to study liquid dielectrophoresis without measuring the droplet contact angle. Furthermore, the unique configuration without any solid-solid contact offers a potential improvement for applications in optics, actuators, and other conventional microelectromechanical systems

Free-Space Permittivity Measurement at Terahertz Frequencies with a Vector Network Analyser

A simple system, based on a vector network analyzer, has been used with new numerical de-embedding and parameter inversion techniques to determine the relative permittivity (dielectric properties) of materials within the frequency range 750–1100 GHz. Free-space (noncontact), nondestructive testing has been performed on various planar dielectric and semiconducting samples. This system topology is well suited for quality control testing in an industrial setting requiring high throughput. Scattering parameters, measured in the absence of a sample, were used to computationally move the measurement plane to the surface of the samples being characterized. This de-embedding process can be completed much faster than a traditional calibration process and does not require exact knowledge of system geometric lengths. An iterative method was developed for simultaneously determining both sample geometric thickness and electric permittivity, through calculation of theoretical scattering parameters at material boundaries. A constrained nonlinear optimization process was employed to minimize the discrepancy between measured transmission and reflection data with this simulated data, in lieu of a closed-form parameter inversion algorithm. Monte Carlo simulations of parameter retrieval in the presence of artificial noise have demonstrated our method’s robustness and superior noise rejection compared with a noniterative method. The precision of derived results has been improved by a factor of almost 50, compared to a closed-form extraction technique with identical input

An ultrathin organic insulator for metal-insulator-metal diodes

The design and fabrication metal-insulator-metal (MIM) diodes using an ultrathin organic insulator are presented. The insulating layer was found to be compact, highly conformal, and uniform, effectively overcoming the main design challenge in MIM diodes. The diodes have strong nonlinear current-voltage characteristics with a typical zero-bias curvature coefficient of 5.4 V-1 and a voltage responsivity of 1.9 kV/W at a frequency of 1 GHz. The fabrication of the diodes only requires only low-temperature processing, which is cost effective, and can potentially be ported to large-area roll-to-roll manufacturing

Computer Aided Patterning Design for Self-Assembled Microsphere Lithography (SA-MSL)

In this paper, we use a finite difference time domain solver to simulate the near field optical properties of self-assembled microsphere arrays when exposed to an incoherent light source. Such arrays are typically used for microsphere lithography where each sphere acts as a ball lens, focusing ultraviolet light into an underlying photoresist layer. It is well known that arrays of circular features can be patterned using this technique. However, here, our simulations show that additional nanometer scale features can be introduced to the pattern by optimising the sphere dimensions and exposure conditions. These features are shown to arise from the contact points between the microspheres which produce paths for light leakage. For hexagonally close packed arrays, the six points of contact lead to star shapes in the photoresist. These star shapes have subfeature sizes comparable to the current achievable resolution of low-cost fabrication techniques