Abstract
Contact-controlled devices, such as source-gated transistors (SGTs), deliberately use energy barriers at the source, and naturally, the positive temperature dependence (PTD) of drain current can be utilized for temperature sensing. We exploit the difference in drain current activation energy, which arises with contact doping in polysilicon n-type contact-controlled transistors, to demonstrate output current with either a PTD or negative temperature dependence (NTD). The range over which output current varies linearly with temperature, as well as the sensitivity, can be tailored by the choice of reference current magnitude and relative source contact properties within the current mirror. The sensing scheme simplifies the circuit design because it relies solely on thin-film transistors and it has inherent immunity to output voltage variation. This ability to tune the sign of temperature dependence allows facile integration in applications requiring homeostasis via feedback, e.g., electronic skin, in a minimal layout area and potentially with convenient reduction of patterning steps during fabrication.
Highlights
E MERGING flexible electronics, such as smart skin [1] or multimodal sensing [2], typically integrate a temperature sensing element, e.g., thermistor, with circuits comprising thin-film transistors (TFTs) [3]
We have previously shown how positive temperature dependence (PTD) and negative temperature dependence (NTD) can be generated by source-gated transistors (SGTs) current mirrors with differing source–gate overlap, S [22]
A comparison of output characteristics [Fig. 2(a) and (b)] for two identical Low-temperature polysilicon (LTPS) SGTs, which only differ in source contact doping, shows, as expected, that a lower contact doping concentration results in higher drain current
Summary
E MERGING flexible electronics, such as smart skin [1] or multimodal sensing [2], typically integrate a temperature sensing element, e.g., thermistor, with circuits comprising thin-film transistors (TFTs) [3]. Functional materials are incorporated in the TFT architecture itself, e.g., pyroelectric gate insulator [4]. While such sensors require uniform and reliable performance [2], the same is required of any adjunct circuit comprising TFTs [5], which have to withstand the challenges of low-cost manufacturing to become commercially viable [6]. Contact-controlled TFTs, such as source-gated transistors (SGTs) [7]–[10], on the other hand, have many features that allow it to stand out as a candidate device for developing compact sensing circuits.
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