Influence of soft x-ray and ultraviolet irradiations on sensitivity of sensors made with piezoelectret films

Abstract

Piezo/ferroelectrets are a kind of cellular electret materials exhibiting piezoelectric effect. Owing to their large piezoelectric activity, flexibility, lightweight, low cost and large area, a list of promising applications have been suggested, including wearable sensors, actuators, micro energy harvesters, and etc. In terms of actual application, one of the most important performance indexes is the stability of piezoelectric response in complex application environments. This article mainly focuses on the influence of soft X-ray and ultraviolet irradiations on piezoelectric sensitivity of two kinds of sensors, made with irradiation cross-linked polypropylene (IXPP) and air-filled parallel-tunnel fluorinated ethylene propylene (FEP) piezoelectret films. A versatile encapsulation process with silica gel for sensor fabrication was introduced to improve the stability against radiations. The results show that soft X-ray irradiation can accelerate the depolarization of the piezoelectrets, while the influence of ultraviolet irradiation on piezoelectrets is not prominent. Encapsulation of the sensors with silica gel may significantly improve their stability under the radiation of soft X-ray. As indicated, the piezoelectric sensitivities of the encapsulated samples, made with IXPP and parallel-tunnel FEP piezoelectret films, are 50.2% and 6.9% of the initial values after 150 min irradiation of soft X-ray with an energy of 9.5 keV, respectively.

Photodiode based on epitaxial silicon for measuring UV emission with a wavelength of 254nm

“…On this layer, a 30 nm thick fluorine-doped tin oxide (SnO2) layer (3) is positioned, with which an ohmic nickel contact (4) up to 1 µm thick is attached. On the reverse side of the crystal, an ohmic common contact layer, also made of nickel (5), up to 1 µm thick, is formed. As shown in Fig.…”

Macro-dipoles in soft/hard expanded-polytetrafluoroethylene + fluoroethylenepropylene (ePTFE + FEP) fluoropolymer-film systems for high-output piezoelectric ferroelectret-transducer applications

“…A range of ferroelectrets that are based on cellularfoam polypropylene (PP) [13,14], polyethylene (PE) [15,16], cyclo-olefin copolymers (COCs) [17], polycarbonate (PC) [14], fluoroethylenepropylene (FEP) copolymers [18,19], sandwiched FEP films or porous polytetrafluoroethylene (PTFE), etc [20], have been developed. There are three main types of internal porous structures following from different fabrication processes: (1) closed lens-shaped pores, as in PP [13], PE [15] and FEP [14] ferroelectrets can be generated by inflating the respective polymer under high-pressure nitrogen or carbon-dioxide gas before heat treatment; charges of opposite polarity are trapped on opposite inner surfaces after poling.…”

“…(2) Artificial cavities can be designed to act as macropores after being charged, e.g. parallel channels in FEP ferroelectrets prepared around templates [18,19], COC ferroelectrets with laser-cut rectangular channel arrays [17]. More recently, 3D printing has become another promising way to prepare ferroelectrets with artificial cavities [21,22].…”