Ž . Sensors and Actuators 82 2000 69–73 www.elsevier.nlrlocatersna A new concept for a self-testable pressure sensor based on the bimetal effect A. Cozma Lapadatu a,b, ) , D. De Bruyker a , H. Jakobsen b , R. Puers a a Katholieke UniÕersiteit LeuÕen, Dept. Elektrotechniek ESAT-Micas, Kardinaal Mercierlaan 94, 3001-HeÕerlee, Belgium b SensoNor asa, KnudsrødÕeien 7, P.O. Box 196, 3192-Horten, Norway Received 8 June 1999; received in revised form 1 October 1999; accepted 4 October 1999 Abstract This paper presents a ‘double-membrane pressure sensor’, with integrated self-test. One membrane is used as the pressure sensitive element, combining the capacitive and the piezoresistive sensing principles. The other one is a bimetallic actuator, involving a siliconraluminium pair, which is used to check the operation of the pressure sensor. The two functions, pressure sensing and actuation, are separated in order to improve the device efficiency and to reduce the negative thermal effects. A diffused meander situated under the thick metal layer serves as a heating resistor. Applying current to this resistor determines the movement of the composite membrane, and consequently, a pressure change in the reference cavity. The output of the pressure sensor changes according to the new differential pressure applied on its membrane. The comparison between the magnitude of this change and the expected value provides information about the correctness of the sensor behaviour. The design of the new structure, the main issues of the fabrication process and experimental results on the self-test function are presented. q 2000 Elsevier Science S.A. All rights reserved. Keywords: Pressure sensor; Self-test; Actuation; Bimetallic effect 1. Introduction By using a built-in actuator, a test system has been conceived to check the functionality of a pressure sensor and, hence, to improve the reliability of the pressure measurement. Beside the sensor itself, there is an actuator that can be activated independently. It performs an actua- tion of the sensor’s pressure sensitive membrane, which is equivalent to applying a supplementary pressure pulse. The change in the sensor’s output of the sensor as a response to this known stimulus provides information on the correct- ness of its behaviour. Self-testing by an actuation process has been reported for accelerometers. The most known example is the one wx that uses the electrostatic actuation for this purpose 1. wx Another one is self-testing by thermal actuation 2 . Self- ) Corresponding author. SensoNor asa, Knudsrødveien 7, P.O. Box 196, 3192 Horten, Norway. Tel.: q 47-33-03-50-79; fax: q 47-33-03-51- 05. Ž . E-mail address: adriana.lapadatu@sensonor.no A.C. Lapadatu . testable pressure sensors were presented in our previous w x publications 3,4 . An obvious requirement is that the actuator itself and the actuation process do not have a negative influence on the pressure sensor. The testing pressure pulses must be high enough to be sensed by the sensor and they must not be dependent on the input pressure signal. A low power consumption, fast response, compatibility between the fab- rication technologies of the actuator and the sensor, and preferably a low size of the resulting system are other criteria that determine the choice of the actuation principle. The electrostatic and the thermo-pneumatic actuations, applied directly on the pressure sensitive diaphragm, were w x presented in previous publications 3,4 . The dimensions of that diaphragm were determined by the requirements for an optimum pressure sensitive device, that is, for a best trade-off between sensitivity and linearity. It was shown that the displacements, which can be produced by the electrostatic forces, are rather small for low actuation voltages, and therefore, so are the pressure pulses that can be simulated. Heating the air inside the cavity of the 0924-4247r00r$ - see front matter q 2000 Elsevier Science S.A. All rights reserved. Ž . PII: S0924-4247 99 00311-8