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Advancements in materials and technologies have enabled thin-film electronics to be directly developed on previously unsuitable substrates. This article explores the fabrication of two thin-film temperature sensors, thermistors, and resistance temperature detectors (RTDs), using stone-based substrates, including marble, brick, stone paper, and Limex paper. The thermistors and RTDs were fabricated utilizing Cu/InGaZnO and Zn, applying the sputtering deposition technique. The sensor’s performance was analyzed based on two different heating methodologies: one using a hotplate, and the other using localized heating from above. The sensors’ performance was characterized within a temperature range of $25~^{\circ }$ C– $80~^{\circ }$ C. While the marble thermistor demonstrated the highest sensitivity among all thermistors at −11.54% $^{\circ }\text {C}^{-1}$ , the stone paper RTD similarly showed the highest sensitivity among all RTDs at 0.064% $^{\circ }\text {C}^{-1}$ . The localized heating methodology on top of RTDs resulted in the stone paper and Limex showing negligible hysteresis. Moreover, the sensors demonstrated stable behavior in the multiple reliability tests. Furthermore, Zn-based RTDs were dissolvable in less than 36 h. The outcomes show that stone-based materials are promising natural eco-friendly substrates for temperature sensors leading to less hazardous electronic waste.

Thin-film transistors (TFTs) play a vital role in flexible electronics. Here, vacuum-processed amorphous indium-gallium–zinc-oxide-based TFTs are fabricated on a $50~\mu $ m thick polyetheretherketone (PEEK) flexible substrate. The ac and dc performances of TFTs with channel length down to $3~\mu $ m are studied. The devices exhibit effective mobility, threshold voltage, and on-/off-current ratio 19.6 cm $^{{2}} \cdot $ V $^{-{1}} \cdot $ s $^{-{1}}$ , 2.9 V, and ${3} \times {10}^{{10}}$ , respectively. To address device stability, bias stress tests are performed, resulting in the maximum variation in the threshold voltage of +0.3 and −0.6 V for a gate voltage stress of +5 and −5 V, respectively, applied for 10 min. The ac performances of InGaZnO (IGZO)-based TFT on this substrate are reported for the first time. Here, the measured unity gain current frequency and unity gain power frequency are 5.4 and 28.5 MHz. Additionally, the TFTs stay fully functional when bent to radii as small as 3 mm exhibiting only minor mobility and threshold voltage variations of +0.4% and −0.2 V. After a dynamic bending test up to 5000 cycles, the mobility and threshold voltage of the TFT deviate by +12.9% and +0.2 V, respectively. These results demonstrate that biocompatible PEEK is a potential substrate for the realization of future unobtrusive wearable systems.

Wearable, flexible, lightweight, and large-area electronics, able to adapt to arbitrary shapes, is a recent technology that promises to integrate sensing and data processing capabilities into everyday objects. This will allow connecting the digital and the physical worlds we live in and enable new innovative applications such as intuitive interfaces and smart textiles for continuous health and safety monitoring. Different technologies, including devices based on organic semiconductors and conventional silicon, are used to develop such wearable systems, however, devices made from novel oxide-based semiconductors currently have one of the best changes to result in electronic systems with sufficient electrical performance on flexible and large-area substrates. Yet, these exciting possibilities come at a price. If all the objects and surfaces around us are equipped with electronic sensor systems, these objects themselves transform into electronic devices, which in turn would massively increase the amount of electronic waste at the end of their lifetime. The same is true for plastic waste as currently most unobtrusive electronics are fabricated on polymer substrates. Furthermore, electronics that are operated near the human body must be safe and biocompatible. The perfect solution for these problems would be to fabricate electronics using environmentally friendly materials and processes, and to guarantee that the electronic components, after fulfilling their intended task, dissolve into their basic constituents, which are then entirely passive or safely absorbed into the nutrient cycle of our environment. Such transient and bioresorbable behavior has been demonstrated for several types of devices but is an underdeveloped approach in the field of oxide semiconductors. Here, motivations and challenges to combine the excellent electrical and mechanical properties of flexible oxide electronics with the environmental friendliness of bioresorbable electronics are explored. This is done by using the most important active building block of such electronics, namely, the TFT, as a model device (Figure 1). Besides assessing the various definitions of biocompatibility and environmental friendliness used in today’s research, the available classes of suitable materials and their impact in the electrical and environmental domain are described. Finally, an evaluation of how such materials can be integrated into working oxide transistors and which performance levels are achievable by these first examples of sustainable oxide TFTs is presented.

This study explores the performance tuning of flexible InGaZnO (IGZO) thin-film transistors (TFTs) using a double-gate configuration. DC analysis on individually controllable double-gate TFTs highlights that the bottom-gate biasing is highly effective in facilitating efficient switching of the devices, whereas the top-gate biasing allows for controlling their performance. This is demonstrated for the ac response of the devices with different channel lengths showing the tunability of ${f}_{\,\text {T}}$ and ${f}_{\,\text {MAX}}$ with a maximum relative tuning up to 130% for ${f}_{\,\text {T}}$ and 170% for ${f}_{\,\text {MAX}}$ . A more efficient control is observed for longer TFTs, resulting in increased characteristics frequency up to 50%. Furthermore, the effect of the performance tunability is also reported even when the double-gate TFTs are exposed to tensile strain induced by a bending radius of 2 mm. These findings indicate new possibilities for the design of flexible analog systems with dynamically adjustable performance.

The AC performance of flexible TFTs sufferers from parasitics caused by tolerances needed for the fabrication on free-standing plastic foils. In this context, the semiconductor island can either be wider or narrower than the source/drain contacts. Traditionally, the second configuration is expected to result in faster TFTs as the total gate overlap area is smaller. However, here it is shown that $\mathrm {2.5~ \mu \text {m} }$ long flexible InGaZnO TFTs with wide semiconductor islands exhibit better frequency performance such as a ${f}_{T}$ of $\mathrm {26.1~ \text {M} \text {Hz} }$ (compared to ${f}_{T}$ of $\mathrm {13.8~ \text {M} \text {Hz} }$ of TFTs with narrow semiconductor islands). This effect is confirmed for flat and bend TFTs and is caused by current spreading in the semiconductor islands, as well as the frequency dependency of the gate capacitance.