electrodes, whose capacitance changes under pressure due to the deformation of the dielectric layer. Although capacitive pressure sensors have some advantages including simple device structure and easy fabrication, they typically exhibit low sensitivity and also require more sophisticated readout circuits that can measure very small capacitance change (typically in the range of hundreds of femtofarad). Moreover, parasitic capacitance and crosstalk between the pixels could also lead to reduced sensitivity and spatial resolution. Piezoelectric materials such as polyvinylidene difluoride that can generate electrical charges from mechanical impact can also be used for pressure sensing. [19] However, such piezoelectric sensors are not suitable for measuring static pressure as they only respond to dynamic changes in pressure. Considering the above, resistive pressure sensors are more promising as they typically offer great sensitivity and only require very basic readout circuit that can measure resistance change. The resistive pressure sensors are typically made using thin films of conductors, such as nanocomposites [15] or nanowires, [16] whose electrical resistance changes under mechanical strain due to microscopic change in morphology or increase in distance between the conductive fillers. [21][22][23] For sensor fabrication, inkjet printing [24][25][26][27][28][29][30][31][32][33] has been widely used and the advantages are multifold. First, the printing process greatly simplifies the fabrication by completely eliminating the need for masks (used in photolithography), as well as high temperature or high vacuum processes commonly used in semiconductor microfabrication. Moreover, it is an additive and highly scalable process that can greatly reduce materials waste. For these reasons, the inkjet printing process could allow the sensors to be low-cost and potentially disposable. Many types of printed sensors including strain sensor, [29][30][31] temperature sensor, [24,32] and humidity sensor [27,28] have already been demonstrated.We have recently demonstrated the use of inkjet-printed silver nanoparticle (AgNP) pattern on an elastomer substrate as an ultrasensitive strain sensor. [31] Inspired by the capability of using printed AgNP thin film for strain sensing and its very high sensitivity, in this work, we demonstrate a printed resistive pressure sensor whose sensing mechanism is based on pressure-induced strain. The sensor consists of a conductive AgNP layer that is directly printed onto a polydimethylsiloxane (PDMS) substrate and subsequently encapsulated by Soft pressure sensors may find a wide range of applications in soft robotics, biomedical devices, and smart wearables. Here, an inkjet-printed resistive pressure sensor that offers high sensitivity and can be fabricated using a very simple process is reported. The device is composed of a conductive silver nanoparticle (AgNP) layer directly printed onto a polydimethylsiloxane substrate and encapsulated by a VHB tape. The pressure is measured through change in e...

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The recent development on wearable and stretchable electronics calls for skin conformable power sources that are beyond current battery technologies. Among the many novel energy devices being explored, triboelectric nanogenerator (TENG) made from intrinsically stretchable materials has a great potential to meet the above requirement as being both soft and efficient. In this paper, we present a lithography-free and low-cost TENG device comprising a porous-structured PDMS layer and a stretchable PEDOT:PSS electrode. The porous PDMS structure is formed by using self-assembled polystyrene beads as the sacrificial template and it is highly ordered with great uniformity and high structural stability under compression force. Moreover, the porous PDMS TENG exhibits improved output voltage and current of 1.65 V and 0.54 nA compared to its counterpart with non-porous PDMS with 0.66 V and 0.34 nA. The effect of different loading force and frequency on the output response of the TENG device has also been studied. This work could shed light on diverse structural modification methods for improving the performance of PDMS-based TENG and the development of intrinsically stretchable TENG for wearable device applications.

Epitaxy of single-crystalline materials laid the foundation for numerous electronics as a core technology. Nevertheless, because the single-crystalline epilayers are covalently bonded to substrates, only limited applications were explored. The recent development of layer transfer techniques has suggested another way involving the production of freestanding membranes that are free from substrates. In this review, we comprehensively catalog recent advances for freestanding-membrane-based electronics from transistors and memory storage to sensors and energy harvesters. We highlight their unique advantages, including flexibility, unique physical coupling, heterointegrability, and costeffectiveness, and summarize their challenges and perspectives.