EHD printing of PEDOT: PSS inks for fabricating pressure and strain sensor arrays on flexible substrates

Abstract

Robotic skins with multi-modal sensors are necessary to facilitate better human-robotic interaction in non-structured environments. Integration of various sensors, especially onto substrates with non-uniform topographies, is challenging using standard semiconductor fabrication techniques. Printing is seen as a technology with great promise that can be used for sensor fabrication and integration as it may allow direct printing of different sensors onto the same substrate regardless of topology. In this work, we investigate Electro-Hydro-Dynamic (EHD) printing, a method that allows printing of micron-sized features with a wide range of materials, for fabricating pressure sensor arrays using Poly(3,4-ethylenedioxythiophene):Polystyrene Sulfonate (PEDOT:PSS). Fabrication of such sensors has been achieved by prepatterning gold or platinum metallized interdigitated comb electrode arrays on a polyimide substrate, with three custom made PEDOT:PSS based inks printed directly onto the electrode arrays. These three inks include a formulation of PEDOT:PSS and NMP; PEDOT:PSS, PVP, and NMP; and PEDOT:PSS, PVP, Nafion, and NMP. All these inks were successfully printed onto sensor elements. The initial results of bending-induced strain tests on the fabricated sensors display that all the inks are sensitive to strain. This confirms their suitability for pressure and strain sensor applications; however, the behavior of each ink; including sensitivity, linearity, and stability; is unique to the type.

Piezoresistive pressure sensor array for robotic skin

“…Results also show high temperature sensitivity, therefore in future work we will need to compensate this effect either by monitoring the temperature of the ambient environment using a temperature sensor or by using two strain gauges on the Wheatstone bridge. More printed arrays samples need to be tested and several derivative inks of PEDOT:PSS should be experimentally evaluated [29]. AS shown in Figure 6, for this paper we printed lines parallel to traces.…”

“…PEDOT:PSS is a conductive and transparent polymer that is stretchable, highly ductile and environmentally stable [29]. It has been used as smart textiles [21], flexible piezoresistive strain gauge sensors [22][23] and touch sensors [24].…”

Study of Partially Transient Organic Epidermal Sensors

“…Combining all-organic electronic and transient technologies, an intrinsically soft functional PEDOT:PSS electrode was electrohydrodynamic-jet (E-jet)-printed onto a water-soluble polyethylene oxide (PEO) substrate. PEDOT:PSS was applied as a functional layer for its desired properties, such as high conductivity [27,[33][34][35], chemical stability [33,36,37], printability [38][39][40][41], and noncytotoxicity [42,43]. A polyethylene oxide (PEO) film was used as a substrate for its hydrophilicity, biocompatibility, and flexibility attributes [43].…”

“…A polyethylene oxide (PEO) film was used as a substrate for its hydrophilicity, biocompatibility, and flexibility attributes [43]. E-jet printing was applied as the fabrication technique because of its high-resolution [44,45], low-cost [46], and drop-on-demand-printing [41,47] characteristics. In this study, the mechanical and electrical properties, along with the transiency, of the epidermal sensor were investigated.…”

Adaptive physical human-robot interaction (PHRI) with a robotic nursing assistant.

“…Also, the gauge factor of PEDOT:PSS was reported to be 17.8 ± 4 which is greater than the metallic strain gauges available commercially [68]. Since the printing was carried out using a PEDOT ink with a process known as Electro-Hydro-Dynamic (EHD) printing, our gauge factor is not fully known at this time, as a result, large numbers of printed sensors were recently fabricated and experimentally characterized [69] [70].…”