Contact Doping as a Design Strategy for Compact TFT-Based Temperature Sensing

Abstract

Contact-controlled devices, such as sourcegated 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.

Organic Source‐Gated Phototransistors with > 104 Photo‐To‐Dark Current Ratio in the Visible Range at Zero Gate‐Source Bias

“…This is important for the development of wearable applications, as supply rails are likely to be regulated to 3.3 V or fed directly from a 3.7 to 4.3 V lithium secondary battery in many internet of things (IoT) applications. [ 32 ] While the PDCR here is lower than the value of 10 9 reported by Milvich et al., [ 7 ] the integration time here was much shorter. It would be interesting, as a next step, to see how Cu and Ni OPSGTs compare to other DNTT OPTs [ 6,15 ] in response to illumination at the peak wavelength of 450 nm.…”

“…[ 14,31 ] As the human‐body temperature is ≈310 K, the DNTT OSGTs would be suitable for use in smart tattoos or wearables for indoor healthcare monitoring, with relatively low variation in their static electrical characteristics for on‐skin or implantable uses. [ 32,33 ]…”

“…[14,31] As the human-body temperature is ≈310 K, the DNTT OSGTs would be suitable for use in smart tattoos or wearables for indoor healthcare monitoring, with relatively low variation in their static electrical characteristics for on-skin or implantable uses. [32,33] Finally, the activation energy E A (calculated using Equation (2) in Experimental Methods at a temperature interval from 290 to 305 K, before mobility-related changes come into play) of OSGTs (Figure 2h) provides information on the behavior of the barrier during operation. Indeed, we see that the height of the barrier in the Cu-contact devices is lower than that in the Ni-contact devices, despite non-uniformity.…”

Extraordinarily Weak Temperature Dependence of the Drain Current in Small‐Molecule Schottky‐Contact‐Controlled Transistors through Active‐Layer and Contact Interplay

“…In contrast, contact-controlled transistors rely on energy barriers at the source contact, and a reduction of these energy barriers is detrimental to their operation. While the high temperature dependence of SGTs can be exploited for temperature sensing [15] or highly compact circuits for regulating temperature, [15,53] in general, technologists might be reluctant to implement these devices, as circuits require stable operation of individual devices they comprise. Currentmode driving is one design solution to this problem.…”