Abstract
Silicon-based digital electronics have evolved over decades through an aggressive scaling process following Moore's law with increasingly complex device structures. Simultaneously, large-area electronics have continued to rely on the same field-effect transistor structure with minimal evolution. This limitation has resulted in less than ideal circuit designs, with increased complexity to account for shortcomings in material properties and process control. At present, this situation is holding back the development of novel systems required for printed and flexible electronic applications beyond the Internet of Things. In this work we demonstrate the opportunity offered by the source-gated transistor's unique properties for low-cost, highly functional large-area applications in two extremely compact circuit blocks. Polysilicon common-source amplifiers show 49 dB gain, the highest reported for a two-transistor unipolar circuit. Current mirrors fabricated in polysilicon and InGaZnO have, in addition to excellent current copying performance, the ability to control the temperature dependence (degrees of positive, neutral or negative) of output current solely by choice of relative transistor geometry, giving further flexibility to the design engineer. Application examples are proposed, including local amplification of sensor output for improved signal integrity, as well as temperature-regulated delay stages and timing circuits for homeostatic operation in future wearables. Numerous applications will benefit from these highly competitive compact circuit designs with robust performance, improved energy efficiency and tolerance to geometrical variations: sensor front-ends, temperature sensors, pixel drivers, bias analog blocks and high-gain amplifiers.
Highlights
F LEXIBLE and printed electronics are maturing from a promising future technology [1]–[5], to be regarded as emerging [6]–[10], with potential areas of use conceived at a rate faster than progress in production-ready applications
We propose a current-starved ring oscillator [53], which adapts its operating frequency according to chip temperature through a negative feedback mechanism, for wide-ranging applications in emerging printed and flexible electronics: thermal safety of the circuit; user comfort and safety; homeostasis
We have demonstrated common source amplifiers and current mirrors with minimal, two-transistor (2T) designs in polysilicon, supported by Silvaco Atlas simulations, as well as current mirrors in IGZO
Summary
F LEXIBLE and printed electronics are maturing from a promising future technology [1]–[5], to be regarded as emerging [6]–[10], with potential areas of use conceived at a rate faster than progress in production-ready applications. For suitably chosen Ci and Cs , abrupt saturation can be achieved This saturation behavior is in contrast with conventional TFT operation, in which the accumulation layer pinches off at the drain at a voltage which can be, in the first order, described as VS AT 2 = VGS – Vth. Drain current results via the transport of charge injected at the source contact through two distinct mechanisms, significantly, the net behavior depends on sourcegate overlap, S [37]. We demonstrate the benefits of implementing wellknown highly compact two transistor (2T) circuits, the common source amplifier and the current mirror, using SGTs (Fig. 1). By realizing these circuits with SGTs, their functionality is substantially improved. The extremely high output impedance leads to behavior close to ideal in both circuits, and the SGT’s inherent temperature sensitivity is exploited for superior circuit functionality
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