Schematic illustration of the explosive view of an e-skin with a 10×10 tactile sensor array and the corresponding optical images

Prof. Xinge Yu's research group at City University of Hong Kong presents materials design and integration scheme as a simple and efficient approach for tactile e-skin with high density of sensing pixels. The materials and devices presented in this work provide insights into the materials science of intrinsically stretchable functional materials, processing routes of stretchable devices and integration strategies of soft sensing arrays, and offer an efficient route for low-cost, large-area, high sensor density e-skin. The work was published on Research (Doi: 10.34133/2020/1085417).

Wearable electronics have attracted great attention around the world in the past decades due to their promising application in health monitoring and human-machine interfaces. Skin-like wearable electronics, also known as epidermal electronics that involves advanced material science and structural designs, exhibits excellent stretchability and multi-functionality, and therefore allows creating electronic skin (e-skin) for the sensation of pressure, humidity, and temperature. Among various sensing capabilities of e-skin, tactile sensing is always the most important part, as which can mimic the basic sensation of skin. To date, many kinds of flexible tactile sensors have been developed based on different working principles, including piezoelectricity, triboelectricity, piezoresistivity and capacitance, however, challenges remain. For instance, piezoresistivity and capacitance type tactile sensors require external power sources, which complicate the integration and may also increase the device size and weight. Self-powered tactile sensors based on triboelectric devices have been a growing interest for wearables and implantable electronics. However, due to the contact-separation working principle in triboelectric electronics, the thickness and stretchability of triboelectric based flexible tactile sensors are still difficult to meet the requirements for e-skin. Meanwhile, signal crosstalk is also a challenge for triboelectric based large-scale tactile sensor arrays.

The reported e-skin by Prof. Xinge Yu's team exploits intrinsically stretchable piezoelectric elastomer as sensing pixels by blending PZT nanoparticles with PDMS. One step screen-printing of the piezoelectric elastomer on the pre-formed in plane electrodes coated soft substrate forms e-skin with high density sensing pixels. Compared to the conventional sandwich structured PZT sensors, the in-plane PZT sensors allow the e-skin exhibits thinner thickness, simpler fabrication process, and greater stretchability. Experimental studies and numerical simulations of both electrical characteristics and mechanical properties of the e-skin prove the sensitive tactile sensing behaviors and excellent durability.

"Electronic Skin from High-Throughput Fabrication of Intrinsically Stretchable Lead Zirconate Titanate Elastomer" was supported by City University of Hong Kong (Grants No. 9610423, 9667199), Research Grants Council of the Hong Kong Special Administrative Region (Grant No. 21210820), Science and Technology of Sichuan Province (Grant No. 2020YFH0181), National Natural Science Foundation of China (Grant No. 11402134), and the Fundamental Research Funds for the Central Universities (Grant No. DUT20RC(3)032). PhD student Yiming Liu, a member of Xinge Yu’s research group, served as the paper's first author.

Tag: Emerging materials research