Systems and methods of operation of capacitive radio frequency micro-electromechanical switches

Abstract

Disclosed are systems and methods of operation for capacitive radio frequency micro-electromechanical switches, such as CMUT cells for use in an ultrasound system. An RFMEMS may include substrate, a first electrode connected to the substrate, a membrane and a second electrode connected to the membrane.

1 . An ultrasound system comprising:
 an ultrasonic array of CMUT cells, each CMUT cell comprising a substrate, a first electrode coupled to the substrate, a flexible membrane at least partially spatially separated from the first electrode, and a second electrode coupled to the flexible membrane;   a voltage supply coupled to the array, wherein the voltage supply is arranged to operate the CMUT cells of the array in a collapsed mode and wherein the voltage supply is adapted to:
 provide a bias voltage and a sequence of pulses of a stimulus voltage to the electrodes of each CMUT cell; and 
   a capacitance sensing circuit adapted, between the applied pulses of the stimulus voltage, to derive an indication of capacitance of at least one of the CMUT cells and to determine an indication of a drift voltage of the CMUT cell based on the indication of capacitance, wherein the drift voltage is a shift or change in the collapse voltage of the CMUT cell.   
     
     
         2 . The ultrasound system as claimed in  claim 1 , wherein the voltage supply is adapted to:
 provide a bias voltage to one of the electrodes of each CMUT cell; and   provide a stimulus voltage to the other of the electrodes of the CMUT cell.   
     
     
         3 . The ultrasound system as claimed in  claim 1 , wherein the capacitance sensing circuit is adapted to:
 generate a test signal, wherein the test signal has a predetermined voltage;   measure an attenuated signal of the test signal, wherein the test signal is attenuated by the impedance of at least the CMUT cell;   determine an impedance of the CMUT cell based on the attenuated signal and the test signal; and   determine the drift voltage of the CMUT cell based on the determined impedance.   
     
     
         4 . The ultrasound system as claimed in  claim 3 , wherein, in responsive to the absolute value of the drift voltage being above a predetermined value, the voltage supply is further adapted to reverse the polarity of the bias voltage. 
     
     
         5 . The ultrasound system as claimed in  claim 3 , wherein, in responsive to the absolute value of the drift voltage being above a predetermined value, the voltage supply is further adapted to reverse the polarity of the stimulus voltage. 
     
     
         6 . The ultrasound system as claimed in  claim 4 , wherein the voltage supply is adapted to reverse the polarity in less than 1 microsecond. 
     
     
         7 . The ultrasound system according to  claim 1 , wherein the second electrode of each CMUT cell is concentric with the first electrode; and
 wherein one of the first and second electrodes comprises a ring, and there is a third electrode which occupies a middle portion of the ring such that the ring and third electrodes are spatially separated.   
     
     
         8 . The ultrasound system according to  claim 2 , wherein the voltage supply is adapted to:
 provide the bias voltage to the first electrode; and   provide the stimulus voltage to the second electrode of the CMUT cell.