Gigahertz Large-Area Electronic Devices for Wireless Applications

Jun 18, 2024, 2:00 pm3:30 pm



Event Description

Future wireless networks envision a large-scale deployment of densely distributed wireless nodes. Those nodes are preferably associated with physical objects such that the rich contextual information can be collected and then utilized. This motivates wireless modules with low power consumption for adequate operation lifetime, and high spatial resolution for accurate node addressing. Large-area electronics (LAE) is a promising technology for this purpose due to its large-area and flex compatibility, while the mainstream electronic technologies (e.g., Si-CMOS and III-V semiconductors) are hindered by limited achievable chip size and rigid form factor. However, due to the low mobility caused by the low-temperature fabrication process and the smallest accessible feature size limited by large-area photolithography, the operation frequency of conventional LAE devices has been restricted to ~10-100 MHz, far below the gigahertz (GHz) regime commonly used in wireless communication. 

The present thesis demonstrates GHz LAE for practical wireless applications, achieved by co-design of device, circuit, and system. 

First, at the device level, this work demonstrates self-aligned zinc-oxide (ZnO) thin-film transistors (TFTs) with unity-power-gain frequency exceeding 3 GHz, which is among the highest reported for metal-oxide TFTs with large-area and flex compatibility. Compact and accurate small-signal TFT models valid at GHz frequencies are developed. They incorporate the delay in TFT channel caused by non-quasi-static effect and the losses from TFT channel resistance. Besides, this work presents flex-compatible large-area planar inductors with record-high quality factors of up to ~65 in the 2.4-GHz wireless band. 

Second, LAE-based radio-frequency switches are enabled by the resonant operation of ZnO TFTs and high quality-factor LAE inductors. These switches feature a high OFF-to-ON impedance ratio of ~48 in the 2.4-GHz wireless band, sufficient for effective signal switching at microwave frequencies. 

Finally, using these GHz LAE devices and circuits as foundational building blocks, two LAE-based wireless systems operating in the 2.4-GHz wireless band are demonstrated: 

  1. a passive backscattering tag with beamforming capability and zero static power; 
  2. a reconfigurable antenna with tunable directionality and operation frequency.

Advisers: James Sturm & Naveen Verma