Highly Sensitive Pressure Sensor Based on Bioinspired Porous Structure for Real‐Time Tactile Sensing

Abstract

A flexible pressure sensor with high performances is one of the promising candidates for achieving electronic skins (E‐skin) related to various applications such as wearable devices, health monitoring systems, and artificial robot arms. The sensitive response for external mechanical stimulation is fundamentally required to develop the E‐skin which imitates the function of human skin. The performance of capacitive pressure sensors can be improved using morphologies and structures occurring in nature. In this work, highly sensitive capacitive pressure sensors based on a porous structure of polydimethylsiloxane (PDMS) thin film, inspired on the natural multilayered porous structures seen in mushrooms, diatoms, and spongia offilinalis, have been developed and evaluated. A bioinspired porous dielectric layer is used, resulting in high‐performance pressure sensors with high sensitivity (0.63 kPa−1), high stability over 10 000 cycles, fast response and relaxation times, and extremely low‐pressure detection of 2.42 Pa. Additionally, the resulting pressure sensors are demonstrated to fabricate multipixel arrays, thus achieving successful real‐time tactile sensing of various touch shapes. The developed high‐performance flexible pressure sensors may open new opportunities for innovative applications in advanced human‐machine interface systems, robotic sensory systems, and various wearable health monitoring devices.

Rough‐Surface‐Enabled Capacitive Pressure Sensors with 3D Touch Capability

“…Initially, S of the 100 wt% PDMS‐coated paper‐based capacitive pressure sensor, whose surface was flat (as observed in Figure c), was measured to be 0.004 kPa −1 in the 0–11 kPa range (Figure a). In contrast, S of the 40 wt% PDMS‐coated paper‐based capacitive pressure sensor was 0.62 kPa −1 for pressures below 2 kPa (Figure a), which is comparable to the sensitivities of sophisticated microfabricated pressure sensors . In addition, we evaluated the sensitivities of various capacitive pressure sensors fabricated on different types of paper using identical PDMS conditions (Figure S8, Supporting Information).…”

“…Among paper‐based electronic devices, flexible pressure sensors have been widely investigated because of their potential application for wearable skins, diagnostics, microelectromechanical system sensors, and human motion detection . Microstructured capacitive pressure sensors, which use compressible microstructural deformations and an effective increase of the dielectric constant, have been developed for use as high‐performance flexible pressure sensors with sensitive responses to external stimulation . Various fabrication techniques have been established for these devices, which can be categorized as (i) synthetic approaches, in which elastomeric foams that contain entrapped air enhance the compressibility and sensitivity; (ii) lithographic approaches, in which microfabricated pyramidal or porous structures enhance the response and relaxation time as well as sensitivity; or (iii) hybrid approaches, in which active devices such as transistors are interfaced with the microstructured elastomer as gate dielectrics, resulting in high sensor performance because of the superlinear characteristics of the transistor .…”

“…Microstructured capacitive pressure sensors, which use compressible microstructural deformations and an effective increase of the dielectric constant, have been developed for use as high‐performance flexible pressure sensors with sensitive responses to external stimulation . Various fabrication techniques have been established for these devices, which can be categorized as (i) synthetic approaches, in which elastomeric foams that contain entrapped air enhance the compressibility and sensitivity; (ii) lithographic approaches, in which microfabricated pyramidal or porous structures enhance the response and relaxation time as well as sensitivity; or (iii) hybrid approaches, in which active devices such as transistors are interfaced with the microstructured elastomer as gate dielectrics, resulting in high sensor performance because of the superlinear characteristics of the transistor . To this end, we recently introduced microstructured resistive pressure sensors and demonstrated their reflective‐type color display upon pressure loading through modulation of the resistance in a pyramidal electrical switch .…”

“…Second, the 40 wt% PDMS film conformably coats the rough surface of the graphite‐covered paper such that the roughness is preserved (Figure S11, Supporting Information). This roughness enables the formation of a small airgap in an equivalent manner as a microstructured periodic surface or porous PDMS, allowing sensitive response in the low‐pressure region. In a series of experiments in which unpolished silicon wafer‐ ( R c ≈ 2 µm), pristine paper‐ ( R c ≈ 800 nm), and blu‐ray ( R c ≈ 70 nm)‐molded rough PDMS surfaces were prepared on flat indium tin oxide (ITO) electrodes (Figure S12, Supporting Information) to clarify the effect of the rough surface of the PDMS layer on the sensitivity, the resulting sensitivities of 0.18, 0.10, and 0.10 kPa −1 , respectively, were indeed higher than that of the 100 wt% flat PDMS (Figure b).…”

Emergent Soft Lithographic Tools for the Fabrication of Functional Polymeric Microstructures

“…[103]); 3D masters (Adapted with permission from Ref. [108]); Dynamic masters (Scale bars are 50 μm. Adapted with permission from Ref.…”