Patent Publication Number: US-7586238-B2

Title: Control and testing of a micro electromechanical switch having a piezo element

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is related to a commonly assigned, co-pending application by Lianjun Liu et al. entitled, “Control and Testing of a Micro Electromechanical Switch,”, and filed concurrently herewith. 
     The present application is related to a commonly assigned, co-pending application by Lianjun Liu entitled, “Piezoelectric MEMS Switches and Method For Making”, having application Ser. No. 11/363,791, and filed on Feb. 28, 2006. 
     FIELD OF THE INVENTION 
     The present invention relates generally to micro electromechanical systems (MEMS), and more particularly, to sensing, control and testing of a MEMS switch having a piezo element. 
     RELATED ART 
     Micro electromechanical switches can be used in telecommunications systems to switch radio frequency (RF) signals. It is important for the MEMS switches to function reliably. A MEMS switch may fail closed, for example, due to stiction. A micro electromechanical switch may be used to couple a RF transmitter and a receiver to an antenna. A first switch is used to couple the receiver to the antenna while a second switch is used to coupled the transmitter to the antenna. Generally only the transmitter or the receiver can be coupled to the antenna at one time. If the first switch between the receiver and the antenna failed in the closed position when the second switch is closed, RF power from the transmitter may be fed into the receiver, causing serious damage. Therefore, it would be desirable to be able to detect when a MEMS switch fails to operate. 
     Also, when closing a MEMS switch, the switch may bounce between open and closed positions several times before closing completely. Switch bounce results in increased closing time and decreased reliability of the switch. Therefore, it would be desirable to reduce bouncing of a MEMS switch. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention is illustrated by way of example and not limited by the accompanying figures, in which like references indicate similar elements, and in which: 
         FIG. 1  illustrates a top plan view of a MEMS switch in accordance with one embodiment. 
         FIG. 2  illustrates a cross-sectional view taken along the line  2 - 2  of a portion of the switch of  FIG. 1  with the contacts open. 
         FIG. 3  illustrates a cross-sectional view taken along the line  2 - 2  of the switch of  FIG. 2  with the contacts closed. 
         FIG. 4  illustrates, in block diagram form, an embodiment of a circuit for controlling the switch of  FIG. 1 . 
         FIG. 5  illustrates, in block diagram form, a communications system implementing the circuit of  FIG. 4 . 
         FIG. 6  illustrates a top plan view of a MEMS switch in accordance with another embodiment. 
         FIG. 7  illustrates a cross-sectional view taken along the line  7 - 7  of a portion of the switch of  FIG. 6  with the contacts open. 
         FIG. 8  illustrates a cross-sectional view taken along the line  7 - 7  of the switch of  FIG. 6  with the contacts closed. 
         FIG. 9  illustrates, in schematic diagram form, a detection circuit for use with the switch of  FIG. 6  in accordance with one embodiment. 
         FIG. 10  illustrates, in schematic diagram form, a detection circuit for use with the switch of  FIG. 6  in accordance with another embodiment. 
         FIG. 11  is a flow chart for illustrating a method to close a MEMS switch in accordance with an embodiment of the disclosure. 
         FIG. 12  is a flow chart for illustrating a method to open a MEMS switch in accordance with an embodiment of the disclosure. 
         FIG. 13  is a flow chart for illustrating a method to test a MEMS switch in accordance with an embodiment of the disclosure. 
       Skilled artisans appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help improve the understanding of the embodiments of the disclosure. 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     Generally, the present invention provides a micro electromechanical device having a micro electromechanical switch. The micro electromechanical switch has a movable portion positioned to form an electrical connection between a first electrical contact and a second electrical contact. A piezoelectric electrode is formed on the movable portion. The piezoelectric electrode moves the movable portion in response to a driver voltage. A piezo element is formed on the movable portion of the switch. The piezo element is for detecting movement of the movable portion between an open position and a closed position. The piezo element is also used to detect switch bouncing when the switch transitions from the open position to the closed position. 
     In one embodiment, the piezo element is a piezoelectric element that generates a voltage in response to a mechanical stress caused by movement of the movable portion. In another embodiment, the piezo element is a piezo-resistive element that changes resistance in response to a mechanical stress caused by movement of the movable portion. 
     In another aspect of the disclosed embodiments, a method for controlling a micro electromechanical switch is provided. The micro electromechanical switch has a movable portion positioned to form an electrical connection between a first electrical contact and a second electrical contact. A piezoelectric electrode is formed on the movable portion. The piezoelectric electrode moves the movable portion in response to a driver voltage. The method comprises: providing a piezo element on the movable portion to detect movement of the movable portion; providing the driver voltage to close the switch; detecting movement of the movable portion using the piezo element to determine if the switch is closed; and determining that the switch is closed. 
     Also, in another aspect of the above method, detecting movement of the movable portion further comprises: detecting switch bounce movements of the movable portion using the piezo element; and applying the driver voltage to counter the switch bounce movements. 
     By using a piezo element to sense whether the switch is open or closed, failure of the switch can be discovered. Also, the piezo element can be used to “self-test” the switch during power-up of a device, or between mode or frequency band switching. In addition, by detecting switch bounce, the time for closing the switch is reduced and reliability of the switch is improved. 
       FIG. 1  illustrates a top plan view of a MEMS switch  10  in accordance with one embodiment. Cross-sectional views of switch  10 , taken along line  2 - 2  in  FIG. 1 , are illustrated in  FIG. 2  and  FIG. 3 . In  FIG. 2  switch  10  is illustrated with contacts  26  and  28  open, and in  FIG. 3  switch  10  is illustrated with contacts  26  and  28  closed. 
     Referring to  FIGS. 1-3 , switch  10  is an example of a cantilever type switch and is formed using conventional MEMS manufacturing techniques on a substrate  12 . Switch  10  includes a movable portion  14 , a piezoelectric activation element  21 , a piezoelectric sensing element  25 , a first electrical contact, or shorting bar,  26  and second electrical contacts  27  and  28 . The piezoelectric activation element  21  includes a piezoelectric material  18  formed between a top electrode  20  and a bottom electrode  19 . The piezoelectric sensing element  25  includes a piezoelectric material  22  formed between a top electrode  24  and a bottom electrode  23 . The substrate  12  is a silicon semiconductor substrate in the illustrated embodiment but in other embodiments the substrate  12  may be formed from, for example, Gallium Arsenide, ceramics, or glass. Movable portion  14  is a cantilever beam having one end attached to a support structure and the other end positioned above the substrate  12 . The cantilever beam may include a hinge or flexible portion to allow the shorting bar  26  to move down and make physical contact with electrical contacts  27  and  28  as illustrated in  FIG. 3 . Electrical contacts  13  and  17  receive a driver voltage labeled “VD” for activating piezoelectric activation element  21 . A conductive strip is illustrated in  FIG. 1  between electrical contact  13  and top electrode  20 . Likewise, a conductive strip is coupled between electrical contact  17  and bottom electrode  19 . When driver voltage V D  is applied to electrical contacts  13  and  17 , a stress is generated in piezoelectric material  18  causing the movable portion  14  to bend or flex, thus resulting in the shorting bar  26  making an electrical connection with electrical contacts  27  and  28 . When driver voltage V D  is removed, movable portion  14  returns to the open position as illustrated in  FIG. 2 . Electrical conductors (not shown) are be connected to contacts  27  and  28  in an electrical or electronic circuit for transmitting, for example, an RF signal between a transmitter and an antenna or a receiver and an antenna. In other embodiments, different types of signals may be conducted. Note that in another embodiment, the piezoelectric electrode  18  may be replaced with electrodes to electrostatically open and close switch  10 , as illustrated below in  FIG. 6 . 
     Piezoelectric sensing element  25  is positioned on movable portion  14  to sense movement, or bending, of movable portion  14 . In accordance with generally known piezoelectric characteristics, piezoelectric sensing element  25  generates a voltage in response to a mechanical stress such as flexing or bending. Preferably piezoelectric sensing element  25  is formed using lead zirconate titanate (PZT), but may be formed using other materials having piezo properties. A conductive strip is used to couple top electrode  24  to electrical contact  15 . Likewise, a conductive strip is used to couple bottom electrode  23  to electrical contact  16 . Note that the conductive strip is not illustrated in  FIG. 2  or  FIG. 3 . Electrical contacts  15  and  16  receive a voltage from piezoelectric sensing element  22  labeled “V S ” in response to the flexing or bending of piezoelectric sensing element  25 . 
     When movable portion  14  is moved in response to the application of driver voltage V D , piezoelectric sensing element  25  generates voltage V S . In one embodiment, the generated voltage V S  is used to detect whether switch  10  is open or closed. Detection of whether switch  10  is opened or closed can be used, for example, to determine if switch  10  has failed in the field, and allow measures to be taken to protect sensitive and expensive circuitry. Also, failure detection of switch  10  can be used, for example, during manufacturing testing to improve yields. 
     When movable portion  14  moves to the closed position, or make electrical contact between shorting bar  26  and contacts  27  and  28 , the movable portion  14  may “bounce” several times between open and closed positions before the switch completely closes. These closing transients may result in increased closing time and can reduce reliability of switch  10 . The piezoelectric sensing element  25  can be used to sense the switch bouncing and to provide active damping to reduce bouncing as will be discussed later. 
       FIG. 4  illustrates, in block diagram form, a switch bounce control circuit  75  for controlling switch  10  of  FIG. 1 . Circuit  75  provides active damping for reducing closing transients of switch  10  and includes switch status detection and feedback signal generator circuit  90 , system controller  72 , and switch driver  88 . Switch status detection and feedback signal generator circuit  90  includes amplifier  87  and phase delay circuit  89 . Note that switch status detection and feedback signal generator circuit  90  may also include additional circuits not illustrated in  FIG. 4 . Amplifier  87  has an input for receiving voltage V S  from piezoelectric sensing element  22  ( FIG. 1 ), and an output for providing an amplified version of the relatively small voltage V S . Phase delay circuit  89  has an input coupled to the output of amplifier  87 , and an output for providing a phase delayed output labeled “V PD ”. System controller  72  has an input coupled to the output of phase delay circuit  89 , and an output labeled “ACTIVATION SIGNALS”. Switch driver  88  has an input coupled to the output of system controller  72 , and an output for providing driver voltage V D . Note that system controller  72  and switch status detection and feedback signal generator circuit  90  will receive and provide other signals not illustrated in  FIG. 4 . 
     Circuit  75  provides a negative feedback switch bouncing control system for reducing closing transients of switch  10 . The relatively small voltage V S  is provided each time movable portion  14  bounces. Because voltage V S  from sensing element  25  has the same frequency as the bouncing frequency, a predetermined phase delay is added by phase delay  89  to produce a phase delayed signal V PD . System controller  72  provides activation signals for controlling the opening and closing of switch  10 . In accordance with the illustrated embodiment, the system controller  72  combines the phase delayed activation V PD  with the opening and closing activation signals in a negative feedback arrangement to provide timed activations signals to counter the bounces. The timed activation signals are provided to switch driver  88 . Switch driver  88  provides driver voltage V D  to piezoelectric electrode  18  in response to the timed activation signals. 
       FIG. 5  illustrates, in block diagram form, a communications system  70  implementing the bounce control circuit of  FIG. 4 . Communications system  70  is a simplified embodiment of a multi-band RF transceiver, such as for example, an RF transceiver for use in a multi-band cellular telephone handset. In another embodiment, communications system  70  may include a single-band transceiver. Communications system  70  includes system controller  72 , signal processor  74 , low band RF receiver circuit  76 , high band RF receiver circuit  78 , low band RF transmitter  80 , high band RF transmitter  82 , multiple-tap switch  84 , antenna  86 , switch driver  88 , and switch status detection and feedback signal generator circuit  90 . 
     System controller  72  controls and coordinates the operation of signal processor  74 , receivers  76  and  78 , transmitters  80  and  82 , and switch driver  88 . System controller  72  is bi-directionally coupled to processor  74 , receivers  76  and  78 , and transmitters  80  and  82  for sending and receiving control information. System controller  72  also has an output coupled to an input of switch driver circuit  88  for providing a plurality of control signals labeled “SWITCH CLOSE [0:3]”, an output coupled to an input of switch driver circuit  88  for providing a plurality of control signals labeled “SWITCH OPEN [0:3]”, and an input for receiving a control signal from switch status detection and feedback signal generator circuit  90  labeled “V PD [0:3]”. 
     Processor  74  primarily processes data signals that are received from receivers  76  and  78 , and prepares data for transmission by transmitters  80  and  82 . Processor  74  is bi-directionally coupled to receivers  76  and  78  for receiving the data and for sending and receiving control information. Likewise, processor  74  is bi-directionally coupled to transmitters  80  and  82  for sending the data and for sending and receiving control information. 
     Multiple-tap switch  84  includes 4 MEMS piezoelectric switches labeled “S 0 ” through “S 3 ”. Each of the MEMS switches of multiple-tap switch  84  are functionally similar to switch  10  illustrated in  FIG. 1  and discussed above. However, in other embodiments, multiple-tap switch  84  may include a different type of MEMS switch. For example, switch  11 , illustrated in  FIG. 6-8  and discussed below can be used in communication system  70 . Also, the number of MEMS switches may be different in another embodiment. One terminal of each of the switches S 0 -S 3  is coupled together and to antenna  86 , and the other terminal is coupled to one of the transmitters or receivers as illustrated in  FIG. 5 . In the illustrated embodiment, only one of switches S 0 -S 3  is closed at one time. Switch driver  88  is coupled to multiple-tap switch  84  and provides driver voltages labeled “V DS0 ”, “V DS1 ”, “V DS2 ”, and “V DS3 ” to control activation of each of the switches S 0 -S 3  in response to a corresponding SWITCH OPEN [0:3] or SWITCH CLOSE [0:3] activation signal from system controller  72 . Switch status detection and feedback signal generator circuit  90  includes a plurality of inputs labeled “V S0 ” through “V S3 ” for receiving the sensed voltage for each of the piezoelectric sensing elements of switches S 0  to S 3 . For example, the piezoelectric sensing element of switch S 0  provides the sensed voltage V S0 . When a switch is detected as open or closed, the information is provided to system controller  72  as a corresponding one of signals V PD [0:3]. Switch status detection and feedback signal generator circuit  90  is similar to switch status detection and feedback signal generator circuit  90  of  FIG. 4  except that switch status detection and feedback signal generator circuit  90  includes an amplifier and phase delay circuit similar to amplifier  87  and phase delay circuit  89  for each switch in multiple-tap switch  84 . Also, switch status detection and feedback signal generator circuit  90  may include additional logic and buffer circuits (not shown). 
     To increase switch life, “cold switching” is used by communications system  70 . That is, RF power is only turned on after the switch is closed and before the switch is opened. Cold switching can reduce switch failure due to stiction caused by arcing between the contacts. By way of example, during normal operation of communication system  70 , communication system  70  is receiving low band information from antenna  86 . Switch S 0  is closed, coupling the antenna  86  to low band receiver  76 . The other switches S 1 -S 3  are open. If communication system  70  is required to transmit information using low band transmitter  80 , system controller  72  will first assert control signal SWITCH OPEN  0  to cause switch S 0  to open. Switch status detection and feedback signal generator circuit  90  will detect if switch S 0  actually opened, and if switch S 0  opened, will assert the appropriate one of signals V PD [0:3] to system controller  72 . System controller  72  can then assert control signal SWITCH CLOSE  2  to direct switch driver  88  to provide drive voltage V DS2  to cause switch S 2  to close, thus connecting low band transmitter  80  to antenna  86 . As described above in the discussion of  FIG. 4 , the piezoelectric sensing element of the switch being closed will sense if the closing switch bounces, and provide a phase delayed negative feedback signal to system controller  72 . System controller  72  will then apply activation pulses to prevent, or reduce, the bounce. Once the switch is sensed to be closed, RF power is then turned on by system controller  72  and low band transmitter  80  will transmit an RF signal to antenna  86 . 
       FIG. 6  illustrates a top plan view of a MEMS switch  11  in accordance with another embodiment. Cross-sectional views of switch  11 , taken along line  7 - 7  in  FIG. 6 , are illustrated in  FIG. 7  and  FIG. 8 . In  FIG. 7  switch  11  is illustrated with contacts  26  and  28  open, and in  FIG. 8  switch  11  is illustrated with contacts  26  and  28  closed. 
     Referring to  FIGS. 6-8 , switch  11  is a cantilever type switch and is formed using conventional MEMS manufacturing techniques on a substrate  12 . Switch  11  includes a movable portion  14 , a bottom activation electrode  34 , a top activation electrode  31 , a piezo-resistive sensing element  33 , a first electrical contact, or shorting bar,  26  and second electrical contacts  27  and  28 . The substrate  12  is a silicon substrate in the illustrated embodiment but in other embodiments the substrate  12  may be formed from, for example, Gallium Arsenide, ceramics, or glass. Movable portion  14  is a cantilever beam having one end attached to a support structure and the other end positioned above the substrate  12 . The cantilever beam may include a hinge or flexible portion to allow the shorting bar  26  to move down and make physical contact with electrical contacts  27  and  28  as illustrated in  FIG. 8 . Electrical contact  13  receives a driver voltage labeled “V D ” for activating top activation electrode  31 . When driver voltage V D  is applied, the top activation electrode  31  and the bottom activation electrode  34  function to electrostatically close the switch causing contact  26  to make an electrical connection with contacts  27  and  28 . When driver voltage V D  is removed, the movable portion  14  returns to the open position as illustrated in  FIG. 7 . Electrical conductors (not shown) are connected to contacts  27  and  28  in an electrical or electronic circuit for transmitting, for example, an RF signal between a transmitter and an antenna or a receiver and an antenna when switch  11  is closed. Note that in another embodiment, the top and bottom activation electrodes may be replaced with a piezoelectric activation electrode as discussed above regarding  FIG. 1 . 
     Piezo-resistive sensing element  33  is positioned on movable portion  14  to sense movement of movable portion  14 . Note that even though only one piezo-resistive sensing element  33  is illustrated on movable portion  14 , in other embodiments, more than one may be used. In accordance with generally known piezo-resistive characteristics, a resistance of piezo-resistive sensing element  33  will change in response to being flexed, or bent. Piezo-resistive sensing element  33  is implemented in the silicon of movable portion  14 , and is preferably fabricated as a bridge circuit for improved accuracy and sensitivity. Preferably piezo-resistive element  33  is formed using silicon or thin film polysilicon. In another embodiment, piezo-resistive element  33  may be formed using a different piezo-resistive material. As illustrated in  FIG. 1 , piezo-resistive sensing element  33  is electrically coupled to contacts  15  and  16  using conductive strips to provide a resistance value labeled “R S ” that changes in response to being flexed. Note that the conductive strips are not illustrated in  FIG. 7  or  FIG. 8 . 
     The changing resistance value R S  is used to detect whether switch  11  is open or closed. Detection of whether switch  11  is open or closed can be used, for example, to detect if switch  11  has failed in the field and allow sensitive and expensive circuitry to be isolated before damage can occur. Also, failure detection of switch  11  can be used, for example, during manufacturing testing to improve yields. 
     As discussed above, when movable portion  14  moves to close, or make electrical contact between shorting bar  26  and contacts  27  and  28 , the movable portion  14  may “bounce” several times between the open and closed positions before the switch completely closes. These closing transients may result in increased closing time and can reduce the reliability of switch  11 . The piezo-resistive sensing element  33  can be used to sense the switch bouncing and to provide active damping to reduce bouncing as discussed above regarding  FIG. 4 . 
       FIG. 9  illustrates, in schematic diagram form, a detection circuit  40  for use with the switch of  FIG. 6  in accordance with one embodiment. Detection circuit  40  is used to determine if a MEMS switch such as switch  11  is open or closed. Detection circuit  40  includes resistors  42 ,  44 , and  46 , and signal source  50 . Resistor  42  has a first terminal coupled to a first output terminal  41 , and a second terminal. Resistor  44  has a first terminal coupled to the first terminal of resistor  42 , and a second terminal coupled to sensing electrode terminal  45 . Resistor  46  has a first terminal coupled to the second terminal of the resistor  42 , and a second terminal coupled to both second output terminal  43  and to sensing electrode terminal  47 . Signal source  50  has a first output terminal coupled to the second terminal of resistor  42 , and a second output terminal coupled to the second terminal of the resistor  44 . Signal source  50  provides a time varying, or AC signal labeled “V 1 ”. In the illustrated embodiment, V 1  is time-varying voltage such as a sine wave. In another embodiment, the signal V 1  may be a DC voltage. Resistor  42  has a resistance value labeled “R 1 ”, resistor  44  has a resistance value labeled “R 2 ”, and resistor  46  has a resistance value labeled “R 3 ”. The first and second output terminals provide a voltage labeled “V OUT ”. Piezo-resistive sensing element  33  is coupled to terminals  45  and  47 . In detection circuit  40 , the resistance values of resistors  42 ,  44 , and  46  are chosen so that when the switch is open
   R   1   /R   2   =R   3   /R   S  and V OUT =0. 
When switch  11  closes, R S  becomes larger; the ratio value R 3 /R S  changes, causing V OUT  to be non-zero.
 
     In the illustrated embodiment, detection circuit  40  is preferably implemented on the same substrate as switch  11  as a part of switch status detection and feedback signal generator circuit  90  (illustrated in  FIG. 4  and  FIG. 5 ). This minimizes undesirable parasitic effects from, for example, long conductors such as wire bonds and board traces. However, in other embodiments detection circuit  40  may be implemented on another substrate. 
       FIG. 10  illustrates, in schematic diagram form, a detection circuit  60  for use with the switch of  FIG. 6  in accordance with another embodiment. Detection circuit  60  may be used in, for example, switch status detection and feedback signal generator circuit  90  of  FIG. 4  and  FIG. 5 . Detection circuit  60  includes amplifier  62 . Amplifier  62  has a first input for receiving a reference voltage labeled “V REF ”, a second input coupled to a terminal  64 , and an output for providing an output voltage labeled “V OUT ”. Piezo-resistive sensing element  33  is coupled between terminal  64  and terminal  66 . Terminal  66  is coupled to a power supply voltage terminal labeled “V SS ”. In the illustrated embodiment, V SS  is coupled to ground. In another embodiment, V SS  may be a different power supply voltage. When switch  11  opens and closes the resistance value R S  changes between a low resistance value and a higher resistance value. A corresponding low and high voltage change is provided to the second input of amplifier  62 . The reference voltage V REF  is chosen to be between the high and low voltage provided at the second input of amplifier  62 . Amplifier  62  compares the voltage at terminal  64  to V REF , the voltage V OUT  is determined as a result of the comparison. For example, if the voltage at terminal  64  is higher than V REF , then V OUT  may correspond to a logic one indicating that switch  30  is closed. If the voltage at terminal  64  is lower than V REF , then V OUT  may correspond to a logic zero, indicating that switch  30  is open. 
     Like detection circuit  40 , detection circuit  60  is preferably implemented on the same substrate as switch  30 . This minimizes undesirable parasitic effects from, for example, long conductors such as wire bonds and board traces. However, in other embodiments detection circuit  60  may be implemented on another substrate. 
       FIG. 11  is a flow chart for illustrating a method  100  for closing a MEMS switch in a system in accordance with one embodiment. At step  102 , a command to close a switch is provided by a system controller, such as system controller  72  ( FIG. 5 ). At step  104 , the command is received by a switch driver circuit, such as switch driver circuit  88 . The switch driver provides a drive voltage V D  to close the switch. At decision step  106 , it is determined if the switch is closed. If the detection circuit, such as detection and feedback signal generator circuit  90 , determines that the switch closed, then the YES path is taken to step  108  and RF power is turned on and transmitted through the switch. However, if the switch did not close, the NO path is taken to step  110  where an incremental delay is applied. After the incremental delay at decision step  112 , it is determined if the total accumulated delay is greater than a predetermined delay period “X”. The delay X may be a predetermined multiple of the incremental step  110  delay. If at decision step  112  the accumulated total delay is less than the predetermined delay X, the detection circuit checks the status of the switch by looping around the NO path from decision step  112  to decision step  106  and back to decision step  112 . The incremental delay at step  110  is added to the total delay at step  112 . If the switch closes before the end of the predetermined delay X, then the YES path is taken from step  106  to step  108  and RF power is turned on. However, if the switch fails to close before the end of the predetermined delay X, the YES path is taken from decision step  112  to step  114 . At step  114 , the switch is determined to be failed open, and at decision step  116 , a failure indication is sent from the detection circuit to the system controller. 
       FIG. 12  is a flow chart for illustrating a method  200  to open a MEMS switch in accordance with an embodiment of the disclosure. At step  202  the RF power is first turned off if it is desirable to “cold switch” the MEMS switch. At step  204 , a command to open a switch is provided by the system controller to the switch driver. At step  206 , the switch driver then turns off the driver voltage that holds the switch closed, allowing the switch to open. At decision step  208 , the detection circuit, such as detection circuit  40 , determines if the switch is open. If the switch is open, the YES path is taken from step  208  to step  210 , and the switch driver circuit and detection circuit wait until the next switch activation command. However, if at step  208  it is determined that the switch is still closed, the NO path is taken from step  208  to delay step  212 . As discussed above regarding the method  100  of  FIG. 11 , the step  212  delay is an incremental delay that is accumulated to provide an accumulated delay. At decision step  214 , it is determined if the accumulated delay is greater than a predetermined delay “Y”. If the delay is less than the delay Y, the NO path is taken back to step  208 . If the switch is detected as open, then the YES path is taken from step  208  to step  210 . If the switch is still detected as closed, the method loops around delay step  212 , decision step  214 , and decision step  208  until the accumulated delay is greater than delay Y. If the accumulated delay is greater than delay Y then the YES path is taken from step  214  to step  216 . At step  216  the switch is determined to have failed open and a failure indication is sent at step  218 . 
       FIG. 13  is a flow chart for illustrating a method  300  to test a MEMS switch at, for example, power up, during mode switching, or during manufacturing. At step  302  a command to close a switch is provided by a system controller, such as system controller  72 . At step  304 , the command is received by a switch driver circuit, such as switch driver circuit  88 . The switch driver provides a drive voltage to close the switch. At decision step  306 , it is determined if the switch is closed. If the detection circuit, such as detection and feedback signal generator circuit  90 , determines that the switch closed, then the YES path is taken to step  308 . If at step  306  it is determined that the switch is closed, the NO path is taken to step  310  and an incremental delay is applied to an accumulated delay. At step  312 , it is determined if the accumulated delay is greater than a predetermined delay X. If the accumulated delay is less than delay X, the method loop around steps  306 ,  310 , and  312  until either the switch is detected to be closed, or the delay is determined to be greater than delay X at step  312 . If the delay is greater than delay X and the switch is still open, the YES path is taken from step  312  to step  314 . At step  314  the switch is determined to have failed. A step  326 , the self-test is complete and a negative pass/fail indication is provided. 
     Referring back to step  306 , if the switch is determined to have closed, the YES path is taken to step  308  and a command is provided by the system controller to open the switch. At step  316 , the switch driver circuit turns off the driver voltage to the activation electrodes of the switch and the switch is suppose to open. At decision step  318 , it is determined if the switch opened. If the switch opened the YES path is taken from step  318  to step  326  and the passed indication is provided. If the switch is not detected as opened, the NO path is taken to step  320  and an incremental delay is applied to an accumulated delay. At step  322  it is determined if the accumulated delay is greater than a delay Y. If the accumulated delay is not greater than delay Y, then the NO path is taken to step  318 . Step  318  is repeated via the loop around steps  320  and  322  until the accumulated delay is greater than delay Y. If the accumulated delay is greater than delay Y, the YES path is taken from step  322  to step  324  and the switch is determined to have failed closed. At step  326  a failed indication is provided. 
     The described embodiments provide a detection circuit and method for detecting if a piezoelectric MEMS switch is closed or open. The use of the detection circuit allows for reliable “cold switching” of RF power. Also, the detection circuit and method provides for self-test functionality that can increase the reliability of a system having the detection circuit. In addition, the piezoelectric sensing element can be used in a circuit to detect and reduce switch bounce. 
     In the foregoing specification, the invention has been described with reference to specific embodiments. However, one of ordinary skill in the art appreciates that various modifications and changes can be made without departing from the scope of the present invention as set forth in the claims below. Accordingly, the specification and figures are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of the present invention. 
     Benefits, other advantages, and solutions to problems have been described above with regard to specific embodiments. However, the benefits, advantages, solutions to problems, and any element(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential feature or element of any or all the claims. The terms a or an, as used herein, are defined as one or more than one. The terms including and/or having, as used herein, are defined as comprising (i.e., open language). As used herein, the terms “comprises,” “comprising,” or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.