A large-area, flexible pressure sensor matrix with organic field-effect transistors for artificial skin applications

Abstract

It is now widely accepted that skin sensitivity will be very important for future robots used by humans in daily life for housekeeping and entertainment purposes. Despite this fact, relatively little progress has been made in the field of pressure recognition compared to the areas of sight and voice recognition, mainly because good artificial ''electronic skin'' with a large area and mechanical flexibility is not yet available. The fabrication of a sensitive skin consisting of thousands of pressure sensors would require a flexible switching matrix that cannot be realized with present silicon-based electronics. Organic field-effect transistors can substitute for such conventional electronics because organic circuits are inherently flexible and potentially ultralow in cost even for a large area. Thus, integration of organic transistors and rubber pressure sensors, both of which can be produced by low-cost processing technology such as large-area printing technology, will provide an ideal solution to realize a practical artificial skin, whose feasibility has been demonstrated in this paper. Pressure images have been taken by flexible active matrix drivers with organic transistors whose mobility reaches as high as 1.4 cm 2 ͞V⅐s. The device is electrically functional even when it is wrapped around a cylindrical bar with a 2-mm radius. R ecognition of tactile information will be very important for future generations of robots used by humans in daily life for housekeeping and entertainment purposes (1, 2). An important step to obtain good artificial ''electronic skin'' is to fabricate large-area pressure sensors with mechanical f lexibility. Despite this fact, relatively little progress has been made in the field of pressure recognition compared to the areas of sight and voice recognition (1, 2). Even though f lexible materials such as polymers and rubbers have been used to make sensing components, the fabrication of a sensitive skin consisting of thousands of pressure sensors would also require a f lexible switching matrix that cannot be realized with present-day silicon-based electronics.Organic field-effect transistors (3-13) are inherently f lexible and very inexpensive to fabricate even for large areas (9, 10), and hence are adequate for use as a switching matrix in a pressure sensor. The minimum bending diameter reported so far, however, has been only 30 mm (11) because inorganic materials were still used in many previous transistors for some components such as gate insulators (SiO 2 , Al 2 O 3 ) and base films (glass, silicon). Moreover, the highest mobilities reported so far for plastic transistors have been around 0.1 cm 2 ͞V⅐s (5), much lower than the best values around 2-5 cm 2 ͞V⅐s obtained with hard substrates (13). The above two points have been major hurdles to the application of organic transistors to large-area f lexible electronics.In this article, we demonstrate an application of organic transistors in which all of the materials are soft except the electrodes. The organic transistors are integrated w...

Solution‐Processed Bilayer Dielectrics for Flexible Low‐Voltage Organic Field‐Effect Transistors in Pressure‐Sensing Applications

“…It is noteworthy that high sensitivities in both the low‐ and medium‐pressure regimes were obtained for the OFET‐based sensor at a low operating voltage of −5 V. The operating voltage is much lower than those of the previously OFET‐based pressure sensors reported so far 6, 18, 19, 20, 21, 22, 23, 24. By contrast, the control OFET sensors with a pure PMMA dielectric require a higher operating voltage of −10 V and deliver much lower sensitivities of 0.49 and 0.42 kPa −1 in the low‐ and medium‐pressure regimes, respectively (see Figure S5, Supporting Information).…”

“…To achieve OFET‐based pressure sensors, many efforts have been devoted to designing device structures, optimizing dielectric/semiconductor materials, as well as tuning gate electrodes 6, 18, 19, 20, 21, 22, 23, 24. For instance, Someya et al introduced OFET as a readout element for conductive rubber pressure sensors 18.…”

“…For instance, Someya et al introduced OFET as a readout element for conductive rubber pressure sensors 18. By using microstructured polydimethylsiloxane (PDMS) as the dielectric, Bao and co‐workers developed active OFET sensors for pressure detection,21 and obtained a high sensitivity of 8.2 kPa −1 with fast response time 6.…”

In‐Plane Deformation Mechanics for Highly Stretchable Electronics

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Stretchable electronics represents a relatively recent class of technology [1,2] of interest partly due to its potential for applications in sensory robotic skins, [3,4] conformal photovoltaic modules, [5,6] wearable communication devices, [7,8] skin-mounted monitors of physiological health, [9][10][11] advanced, soft surgical and clinical diagnostic tools, [11,12] and bioinspired digital cameras. [13,14] A key challenge in each of these systems is in the development of strategies in mechanics that simultaneously allow large levels of elastic stretchability and high areal coverages of active devices built with materials that are themselves not stretchable (e.g., conventional metals) and are, in some cases, highly brittle (e.g., inorganic semiconductors).

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Spontaneous High Piezoelectricity in Poly(vinylidene fluoride) Nanoribbons Produced by Iterative Thermal Size Reduction Technique

“…A closer look into the applications of piezoelectricity including biosensing, 3 energy generation, 4À6 pressure sensing, 7 high precision positioning, 8 artificial muscle and skin 9,10 reveals that thermally stable, flexible, and stretchable piezoelectric materials are required to be produced with high yields and in a cost-effective way for the fabrication of commercially feasible, large area, self-powering, and highly efficient devices. Although ceramic piezoelectric materials can present higher piezoelectric coefficients, they suffer from high brittleness, low cyclic endurance, high processing temperature and high production cost as well as toxic elemental composition in contrast to properties of polymer piezoelectric materials.…”