This paper reports on the first low power (10.4 mW) and ultrasensitive linear Hall-effect integrated circuits (LHEICs) using GaAs-InGaAs-AlGaAs 2D electron gas technology. These LHEICs have a state-of-the-art sensitivity of 533 µV/µT and are capable of detecting magnetic fields as low as 177 nT (in a 10-Hz bandwidth), at frequencies from 500 Hz to 200 kHz. This provides at least an order of magnitude improvement in sensitivity and a factor of four improvements in detectability of small fields, compared with commercial Si linear Hall ICs.

This work presents the design, fabrication, and measured results of a fully integrated miniature rectenna using a novel tunnel diode known as the Asymmetrical Spacer Layer Tunnel (ASPAT). The term rectenna is an abbreviation for a rectifying antenna, a device with a rectifier and antenna coexisting as a single design. The ASPAT is the centrepiece of the rectifier used for its strong temperature independence, zero bias, and high dynamic range. The antenna is designed to be impedance matched with the rectifier, eliminating the need for a matching network and saving valuable real estate on the gallium arsenide (GaAs) substrate. The antenna is fully integrated with the rectifier on a single chip, thus enabling antenna miniaturisation due to the high dielectric constant of GaAs and spiral design. This miniaturisation enables the design to be fabricated economically on a GaAs substrate whilst being comparable in size to a 15-gauge needle, thus unlocking applications in medical implants. The design presented here has a total die size of 4 × 1.2 mm2, with a maximum measured output voltage of 0.97 V and a 20 dBm single-tone 2.35 GHz signal transmitted 5 cm away from the rectenna.