Effect of intermitted RIE etching on the beta-PVDF film micro patterning

In recent years, from the viewpoint of Quality of life, minimally invasive surgery using a catheter or an endoscope has been getting a great attention. However, this method has a big problem that is lack of tactile sensation during the surgical procedure so that make the operation become a high degree of difficulty-and the burden on the practitioner is increased. Therefore, if a high sensitivity and high resolution tactile sensor can be attached to the tip of a minimally invasive surgical instruments, palpation becomes possible and the safety of minimally invasive surgery can be improved [1] . There are mainly following three types of tactile sensors:capacitance type, variable resistance type and piezoelectric type. ® Capacitance type is weak against noise, and the circuit design is complicated, and same time there are reliability and cost problem too. ® The resistance variable type has a problem in repeatability due to its hysteresis (hysteresis phenomenon), and it also have problems in stability / reliability and a large of power consumption. © In the piezoelectric type, the sensing feature is that it offers a response only to the dynamic pressure and temperature changes [2] . Because human tactile sensation is originally a dynamic process so that the sensing feature of the piezoelectric type is not a problem, and the effect of temperature can be solved by means of temperature compensation using a temperature sensor. There are mainly two types of piezoelectric materials, one is ceramics and the other is polymer. In ceramics type, lead zirconate titanate (PZT) has been widely used due to its high piezoelectric constants, but PZT is not a good choice as a tactile sensor material in the medical applications because PZT contains harmful material such as lead, and the lack of flexibility, processability and the moldability. In polymer type, polyvinylidene difluoride (PVDF) is mostly used as a sensing material in tactile sensors, because PVDF shows highest piezoelectric constant in polymer, and it is also lightweight, flexible, and biocompatible. In order to apply the tactile sensors to the minimally invasive medical instruments, it is desirable that the sensitivity and resolution could be realized at the level of 1g/mm 2 and 0.2mm [3,4] respectively. Conventional research in tactile sensors has been stayed at the level where electrode patterns are arranged on the surface of the PVDF film [5] . This method causes a crosstalk problem when the pitch of the electrodes became less than 4mm.