Concerted progress in energy sources, sensing, and communications are bringing closer a future in which connected smart sensors will contribute to improved health and sustainable use of resources via environmental, personal health, and process monitoring. For maximum value, data should be generated and processed through means that are reliable, but also cost effective, energy efficient, and ecologically sound. By doing the initial conditioning and processing of incoming data close to the sensor (i.e. at the edge of a sensing network), energy savings and signal integrity can be improved, at the expense of local complexity. The electronic devices performing signal conditioning, data conversion, and decision in such systems are typically realised in state-of-the art and exorbitantly expensive chip manufacturing facilities (fabs).
Recent pressure on the chip supply chain has increased the appeal of exploring alternative technologies. Chief among these are thin-film processes in which electronic devices and sensing components can be manufactured at a fraction of the cost, but simultaneously with: a major drop in performance; challenges in manufacturing circuits of the required complexity; and in many cases, much higher energy requirements during operation.
At Surrey, we have devised and are developing a design philosophy and associated thin-film electronic device called the source-gated transistor (SGT), with superior power efficiency, stability, and amplification compared to conventional thin-film transistors, advantages which come at the cost of further reducing the operating speed. Our recent observation shows that the best SGT performance arises when combining thin semiconductor materials of high electrical permittivity with low-permittivity dielectrics, in a design that is counterintuitive to traditional approaches but is consistent with first principles.
In this project, we will demonstrate SGTs and circuits, with hitherto inaccessible levels of performance and energy efficiency, by combining the advantages of the device architecture with the material properties of suspended crystalline silicon and germanium membranes. The charge carrier mobility of these materials, vastly superior to the usual thin films, and the geometrical scaling afforded by the exceptional SGT functional features, will enable circuits that are >100x faster and >10x more energy efficient than previous SGT-based designs. By expressly merging thin-film and "traditional silicon"-based approaches, these devices will serve as unique building blocks for highly efficient wearable, point-of-care, and distributed sensing systems with built-in sensing, signal conditioning, and decision. Even as we will be using materials aligned with traditional chips, our approach will not rely on the costly state-of-the art fabrication facilities, relieving much needed manufacturing capacity for complex chips e.g. processors and AI accelerators, while delivering transformative functionality to an emerging sensor ecosystem.
In this initial project, the route to manufacturing will be explored, but as a secondary concern. We will focus primarily on the demonstration of a ground-breaking concept, through innovative joining of previously disparate materials and fabrication philosophies. In a high-risk, high-reward approach, we will confirm transistor operation, not only as amplifiers and signal conditioning stages, but potentially as sensors for bio-, chemical and mechanical stimuli. We will establish design rules and guidelines, supported by numerical simulation and by material and device characterisation. Thus, these advances will holistically represent a toolkit for the implementation of highly versatile, multipurpose sensing and processing systems towards a connected future beyond the Internet-of-Things. As a catalyst for prolific academic and industrial advances, the research will contribute firmly to maintaining the UK's leadership in emerging electronic technologies.
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