Traditionally, electronics have been designed with static form factors to serve designated purposes. This approach has been an optimal direction for maintaining the overall device performance and reliability for targeted applications. However, electronics capable of changing their shape, flexibility, and stretchability will enable versatile and accommodating systems for more diverse applications. Here, we report design concepts, materials, physics, and manufacturing strategies that enable these reconfigurable electronic systems based on temperature-triggered tuning of mechanical characteristics of device platforms. We applied this technology to create personal electronics with variable stiffness and stretchability, a pressure sensor with tunable bandwidth and sensitivity, and a neural probe that softens upon integration with brain tissue. Together, these types of transformative electronics will substantially broaden the use of electronics for wearable and implantable applications.

Over the past several decades, tin monoxide (SnO) has been studied extensively as a p-type thin film transistor (TFT). However, its TFT performance is still insufficient for practical use. Many studies suggested that the instability of the valence state of Sn (Sn2+/Sn4+) is a critical reason for the poor performance such as limited mobility and low on/off ratio. For SnO, the Sn 5s–O 2p hybridized state is a key component for obtaining p-type conduction. Thus, a strategy for stabilizing the SnO phase is essential. In this study, we employ a variety of analytical methods such as X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), and Hall measurement to identify the main contributors to the physical properties of SnO. It is revealed that precision control of the process temperature is needed to achieve both the crystallinity and thermal stability of SnO. In other words, it would be ideal to obtain high-quality SnO thin films at low temperature. We find that atomic layer deposition (ALD) is a quite advantageous process for obtaining high-quality SnO thin films by the following two-step process: (i) growth of highly c-axis oriented SnO at the initial stage and (ii) further crystallization along the in-plane direction by a postannealing process. Consequently, we obtained a highly dense SnO thin film (film density: 6.4 g/cm3) with a high Hall mobility of ∼5 cm2/(V·s). The fabricated SnO TFTs exhibit a field-effect mobility of ∼6.0 cm2/(V·s), which is a quite high value among the SnO TFTs reported to date, with long-term stability. We believe that this study demonstrates the validity of the ALD process for SnO TFTs.

Indoor organic photovoltaics (OPVs) are currently being investigated for small-scale energy generation from artificial light sources to power small electronic devices. Despite recent progress in increasing the power conversion efficiency (PCE) of indoor OPVs, the widespread use of expensive indium tin oxide (ITO) as a transparent conducting electrode (TCE) leads to long energy payback times. This study provides a novel and comprehensive description of low-temperature atomic layer deposition (ALD)-processed indium-free tin dioxide (SnO2) films as inexpensive and efficient TCEs for indoor OPVs. These highly conformal and defect-free ALD-fabricated SnO2 films are applied to a poly(3-hexylthiophene):indene-C60 bisadduct-based OPV system. Under 1 sun illumination, an OPV with an SnO2 TCE exhibits limited operational capacity because of the high sheet resistance (~98 Ω sq−1) of the SnO2 layers. However, under a light-emitting diode (LED) lamp with a luminance of 1000 lx, the series resistance, which is related to the sheet resistance, has a marginal effect on the performance of the indoor OPV system, showing a PCE of 14.6 ± 0.3%. A reference OPV with an ITO TCE has a slightly lower PCE of 13.3 ± 0.8% under the same LED conditions. These results suggest that SnO2 TCEs can be efficient and cost-effective replacements for ITO TCEs in indoor OPV systems.

Atomic layer deposition (ALD) is a promising deposition method to precisely control the thickness and metal composition of oxide semiconductors, making them attractive materials for use in thin-film transistors because of their high mobility and stability. However, multicomponent deposition using ALD is difficult to control without understanding the growth mechanisms of the precursors and reactants. Thus, the adsorption and surface reactivity of various precursors must be investigated. In this study, InGaO (IGO) semiconductors were deposited by plasma-enhanced atomic layer deposition (PEALD) using two sets of In and Ga precursors. The first set of precursors consisted of In­(CH3)3[CH3OCH2CH2NHtBu] (TMION) and Ga­(CH3)3­[CH3­OCH2­CH2­NHtBu]) (TMGON), denoted as TM-IGO; the other set of precursors was (CH3)2In­(CH2)3N­(CH3)2 (DADI) and (CH3)3Ga (TMGa), denoted as DT-IGO. We varied the number of InO subcycles between 3 and 19 to control the chemical composition of the ALD-processed films. The indium compositions of TM-IGO and DT-IGO thin films increased as the InO subcycles increased. However, the indium/gallium metal ratios of TM-IGO and DT-IGO were quite different, despite having the same InO subcycles. The steric hindrance of the precursors and different densities of the adsorption sites contributed to the different TM-IGO and DT-IGO metal ratios. The electrical properties of the precursors, such as Hall characteristics and device parameters of the thin-film transistors, were also different, even though the same deposition process was used. These differences might have resulted from the growth behavior, anion/cation ratios, and binding states of the IGO thin films.