A batch fabricated capacitive pressure sensor with an integrated Guyton capsule for interstitial fluid pressure measurement

In this paper, we present the design, fabrication and test of a batch fabricated capacitive pressure sensor with an integrated Guyton capsule for interstitial fluid pressure measurement. The sensor is composed of 12 mu m thick single crystalline silicon membrane and a 3 mu m gap, hermetically sealed through silicon-glass anodic bonding. A novel batch scale method for creating electrical feed-throughs inside the sealed capacitor chamber is developed. The Guyton capsule consists of an array of 10 mu m diameter access holes etched onto a silicon back-plate separated from the silicon sensing membrane by a gap of 5 mu m. The presence of the Guyton capsule (i.e. plates with access holes plus the gap separating them from the sensing membrane) allows for the ingress of interstitial fluid inside the 5 mu m gap following the implantation, thus, providing an accurate measurement of interstitial fluid pressure. The fabricated sensor is 3 x 2 x 0.42 mm(3) in dimensions and has a maximum sensitivity of 10 fF mmHg(-1).