Ultra-Low Energy Electronics

Novel ultra-low energy electronics and devices: 

almost-off-concept

We would like to develop a new form of transistor that which can drastically reduce the power consumption, being based on thin-film technologies, e.g. organics and inorganics. As an example reported in the journal Science, we can use a tiny leakage current conduction in a field effect transistor which is virtually switched off, i.e. in the deep sub-threshold regime – we are calling it ‘Almost-off transistors’. This operational regime is reminiscent of a computer in sleep-mode but which remains active in processing information. To demonstrate the idea, we can employ a thin film transistor based on a semiconducting oxide material (in this case, In-Ga-Zn-O) with a Schottky barrier at the current terminals. Due to the wide energy band-gap of the oxide material, the transistor’s off current was extremely low. Consequently, the transistor’s operating voltage is less than a volt with power consumption below a nanowatt. The beauty of the device lies in its high intrinsic gain (in excess of 400) and infinite output resistance, thanks to the input-output isolation by Schottky barriers created by design. It circumvents the previously unresolved problem of low-temperature processed thin film transistors, i.e. the short channel effect associated with inevitably thick gate insulator and restriction on a gate voltage. These characteristics remain independent of transistor geometry and operating voltage. This family of transistors can be layered on a broad range of substrates ranging from glass and plastic to polyester and paper using low-temperature processes. Oxide materials have already demonstrated their potential in transparent displays, and are a promising candidate for other low cost and large area electronic applications. Because of the ultra-low bias current (< 2pA), a typical battery with 2000 mA-hr specification would have an infinite lifetime (> 0.1 billion years), and thus there is no need to replace or recharge it.

Related key publication:

  • Sungsik Lee and Arokia Nathan, “Subthreshold Schottky-barrier Thin-Film Transistors with Ultralow Power and High Intrinsic Gain,” Science 354 (6310), 302-304, 21 Oct. 2016.

Regarding this area, our research and project scope also covers all aspects of emerging semiconductor technology to minimise power consumption from the levels of materials to devices for circuit design:

  • Device categories:
    • Unipolar device: Field-effect transistors, e.g. MOSFET / MISFET
    • Large area electonic device: Thin-film transistor (TFT)
    • Low cost TFT for non-display applications, analog and digital circuits for wearable sensors in IoT
  • Process technologies and Materials selections:
    • Innovative process for dielectrics, semiconducting layers, metal interconnections, etc.
    • Band-gap engineering, defect control, work-function engineering, etc.
  • Device concepts and architectures:
    • Threshold voltage engineering, sub-threshold slope engineering (e.g. tunnelling barriers), etc.
    • Schottky vs. ohmic contact devices, etc.
    • Sub-threshold operation for ultra low power and high gain, etc.

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