Utilizing Highly Crystalline Pyroelectric Material as Functional Gate Dielectric in Organic Thin‐Film Transistors

Abstract

Since the first description of their use as potential elements for electronic devices, [1] in 1987, organic thin-film transistors (OTFTs) have been intensively studied, due to their potentially lower cost, higher performance, and higher compatibility with flexible electronic applications, as compared to conventional silicon technology. [2][3][4][5] Recently, new functions of OTFTs and their integrated circuits have been being considered, in an attempt to take advantage of organic electronic devices in different applications, such as memory, [6,7] radio-frequency identification (RFID), [8] and sensors. [9][10][11][12] For functional organic devices, organic smart materials with ferroelectric, piezoelectric, and pyroelectric properties can be directly integrated into the OTFT device structure. Good candidates are poly(vinylidene fluoride) (PVDF) and its copolymer with trifluoroethylene, P(VDF-TrFE). The piezo-and pyroelectricity of PVDF and P(VDF-TrFE) were studied in depth, [13][14][15][16][17][18][19][20][21][22] and have been successfully applied in many research fields, [23] but the applications of these properties in OTFTs are limited to external sensing modules. [9,11] On the other hand, there have been both theoretical and experimental reports of memory applications based on the ferroelectricity of P(VDF-TrFE) in OTFTs. [6,7,[24][25][26] High current on-off ratio and fast switching dipoles, which imply a small remnant polarization, are the key aspects in this case. In applications making use of the pyroelectric and piezoelectric properties of P(VDF-TrFE), however, the switching of small remnant polarization should be avoided, and a stable large polarization is required instead. Thus, physical models based on the assumption of small and easy-to-switch remnant polarizations [24][25][26] are not appropriate in interpreting the experimental observation in this work, showing a very large remnant polarization, and need to be modified in order to accurately interpret the experimental information.In this report, we present for the first time the direct use of a highly crystalline P(VDF-TrFE) material with a very large remnant polarization as a pyroelectric gate-insulator layer in an OTFT structure for temperature-sensing applications. This has the advantage of a simpler fabrication process compared to external sensing modules. A poling strategy based on step-wise poling process [20] was required to enhance the effects of the pyroelectricity on the transistor performance (see Experimental). The output characteristics of the OTFTs were changed so as to exhibit a linear current-voltage relationship, thus providing evidence of their large polarization. We introduced a modified transistor equation to fully explain this phenomenon and related problems, such as the effect of the geometry on poling. The thermal behavior of the functional OTFT was also investigated, and the results showed a linear response below the phase transition temperature of P(VDF-TrFE). The temperature response of the device was primarily attributed t...

Flexible and Stretchable Physical Sensor Integrated Platforms for Wearable Human‐Activity Monitoringand Personal Healthcare

“…Reproduced with permission. [ 62 ] Copyright 2009, Wiley-VCH. c) Optical image of a 4 × 4 RTD sensor array laminated on human skin.…”

Advanced carbon materials for flexible and wearable sensors

“…For example, human body temperature is an indicator of fever or other illnesses, or being exposed to a The pyroelectric sensors rely on the pyroelectricity of materials, including Te-nanowire [138], poly(vinylidenefluoride) (PVDF), and P(VDF-TrFE) [139]. Generally, pyroelectric temperature sensors have a relatively high resolution of temperature, but are restricted with long response time and poor flexibility.…”

Infrared optical properties of ferroelectric 0.5BaZr0.2Ti0.8O3–0.5Ba0.7Ca0.3TiO3 thin films

“…As is well known, infrared sensors made of ferroelectric materials exhibit great advantages of uncooled operation, high sensitivity, broad spectral response range and low cost compared with photon detectors and are widely used in alarms, thermal imaging and intruder imaging [4][5][6]. Thin film ferroelectric infrared detectors and focal plan arrays are expected to yield better sensitivities and faster response than equivalent ceramics and bulk single crystals, and can be deposited directly on silicon readout integrated circuitry [7,8].…”