Abstract:
A micro-electromechanical (MEMS) switch includes a substrate, stationary actuator comb teeth extending from a stationary actuator pad supported above the substrate, stationary contact comb teeth extending from a stationary contact pad supported above the substrate, and a body suspended over the substrate for rotation about an axis perpendicular to the substrate. The body includes movable actuator comb teeth interdigitated in-plane with the stationary actuator comb teeth where the shortest distance between adjacent movable and stationary actuator comb teeth has a first value. The body further includes movable contact comb teeth interdigitated in-plane with the stationary contact comb teeth where the shortest distance between adjacent movable and stationary contact comb teeth has a second value smaller than the first value.

Description:
FIELD OF INVENTION 
     This invention relates to a micro-electromechanical (MEMS) switch. 
     DESCRIPTION OF RELATED ART 
     MEMS electrical switches are an alternative to solid state and electromagnetic relay switches. MEMS electrical switches may be used in phase shifters, smart antennas, cell phones, and switchable filters. 
     SUMMARY 
     In one embodiment of the invention, a micro-electromechanical (MEMS) switch includes a substrate, stationary actuator comb teeth extending from a stationary actuator pad supported above the substrate, stationary contact comb teeth extending from a stationary contact pad supported above the substrate, and a body suspended over the substrate for rotation about an axis perpendicular to the substrate. The body includes movable actuator comb teeth interdigitated in-plane with the stationary actuator comb teeth where the shortest distance between adjacent movable and stationary actuator comb teeth has a first value. The body further includes movable contact comb teeth interdigitated in-plane with the stationary contact comb teeth where the shortest distance between adjacent movable and stationary contact comb teeth has a second value smaller than the first value. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings: 
         FIG. 1A  illustrates a MEMS electrical switch in an off state in one or more embodiments of the present disclosure; 
         FIG. 1B  illustrates the MEMS electric switch of  FIG. 1  in an on state in one or more embodiment of the present disclosure; 
         FIG. 2A  illustrates a MEMS electrical switch in an off state in one or more embodiments of the present disclosure; 
         FIG. 2B  illustrates the MEMS electrical of  FIG. 2A  in an on state in one or more embodiments of the present disclosure; and 
         FIG. 3  illustrates a variation of the MEMS electric switch of  FIGS. 2A and 2B  in one or more embodiments of the present disclosure. 
     
    
    
     Use of the same reference numbers in different figures indicates similar or identical elements. 
     DETAILED DESCRIPTION OF THE INVENTION 
       FIGS. 1A and 1B  illustrate a MEMS electrical switch  100  in an off state and an on state, respectively, in one or more embodiments of the present disclosure. Switch  100  can be made using typical semiconductor manufacturing processes. 
     Switch  100  includes a body  102  suspended above a substrate  103  by springs  104  extending from stationary spring pads  106 , which are located above the substrate. Body  102  may have an I-shape where stationary spring pads  106  are nested on the two sides of the web. Springs  104  may be rectangular beams having a small cross-section. The attachment points of springs  104  allows body  102  to rotate about an axis  108  perpendicular to substrate  103 . 
     At one end of body  102 , movable contact comb teeth  110  (only one is labeled) extend out from one flange. Movable contact comb teeth  110  are interdigitated in-plane with stationary contact comb teeth  112  (only one is labeled) extending from a stationary contact pad  114 , which is located above substrate  103 . In one embodiment, adjacent movable and stationary contact comb teeth  110  and  112  are parallel and the shortest distance between them is substantially a distance A. In other words, movable and stationary contact comb teeth  110  and  112  have a substantially uniform gap A between their opposing vertical surfaces. In this embodiment, movable contact comb teeth  110  may have a smaller cross-section than stationary contact comb teeth  112  so the movable contact comb teeth may flex to contact the stationary contact comb teeth substantially along their length. In the figures, hatched areas are stationary. 
     At another end of body  102 , movable actuator comb teeth  116  extend out from the other flange. Movable actuator comb teeth  116  are interdigitated in-plane with stationary actuator comb teeth  118  extending from a stationary actuator pad  120 , which is located above substrate  103 . Together movable and stationary actuator comb teeth  116  and  118  form an actuator for rotating body  102 . In one embodiment, adjacent movable and stationary actuator comb teeth  116  and  118  are parallel and the shortest distance between them is substantially a distance B, which is larger than distance A. In other words, movable and stationary actuator comb teeth  116  and  118  have a substantially uniform gap B between their opposing vertical surfaces. In this embodiment, inherent asymmetry in movable and stationary actuator comb teeth  116  and  118  allows the actuator to rotate body  102  in one direction with electrostatic force when they experience a voltage/electrical potential difference as shown in  FIG. 1B . Inherent asymmetry is introduced by the manufacturing process of switch  100 . In other embodiments, intentional asymmetry is introduced by design to control the rotational direction of body  102 . For example, each movable actuator comb tooth  116  may have substantially uniform gap B with an adjacent stationary actuator comb tooth  118  on its left side and a larger substantially uniform gap C with an adjacent stationary actuator comb tooth  118  on its right side to rotate body  102  in a counterclockwise direction as shown in  FIG. 1B . 
     Stationary contact pad  114  may serve as or be coupled to a source terminal of switch  100 , one stationary spring pad  106  may serve as or be coupled to a drain terminal of the switch, and actuator pad  120  may serve as or be coupled to a gate terminal of the switch. The role of stationary contact pad  114  and stationary spring pad  106  may be reversed. The voltage/electrical potential difference between movable actuator comb teeth  116  and stationary actuator comb teeth  118  may be provided by a voltage source  124  supplying a gate voltage/electrical potential Vg directly or indirectly to stationary actuator pad  120 , and a voltage source  126  supplying a drain voltage/electrical potential Vd directly or indirectly to stationary spring pad  106 . Voltage sources  124  may represent circuitry separate from switch  100  in a larger device, such as a phase shifter, a smart antenna, a cell phone, or a switchable filter. Voltage source  126  may represent circuitry downstream from switch  100  in the larger device. 
     When movable actuator comb teeth  116  and stationary actuator comb teeth  118  rotate body  102 , movable contact comb teeth  110  and stationary contact comb teeth  112  come into contact to close a circuit from one switch terminal to the other (e.g., from pad  114  to pad  106 ). A voltage source  128  may supply a source voltage/electrical potential Vs to stationary contact pad  114  to create a current from the source terminal to the drain terminal. Voltage source  128  may represent circuitry upstream from switch  100  in the larger device. 
       FIGS. 2A and 2B  illustrate a MEMS electrical switch  200  in an off state and an on state, respectively, in one or more embodiments of the present disclosure. Switch  200  can be made using typical semiconductor manufacturing processes. 
     Switch  200  includes a body  202  suspended above a substrate  203  by springs  204  extending from stationary spring pads  206 , which are located above the substrate. Body  202  includes a number of contact and actuator spokes. For example, body  202  includes a first contact spoke  252 , a second contact spoke  254 , and an actuator spoke  256  extending radially from a hub  258 . Spokes  252 ,  254 , and  256  may be evenly spaced around hub  258 . Springs  204  may be rectangular beams having a small cross-section. The attachment points of springs  204  to hub  258  allow body  202  to rotate about an axis  208  perpendicular to substrate  203 . Springs  204  may be evenly spaced around hub  258  where each is located between two spokes. 
     At the end of first contact spoke  252 , movable contact comb teeth  210  extend from a tangent member  260  to the spoke. Movable contact comb teeth  210  are interdigitated in-plane with stationary contact comb teeth  212  extending from a stationary contact pad  214 , which is located above substrate  203 . In one embodiment, adjacent movable and stationary contact comb teeth  210  and  212  are parallel and the shortest distance between them is substantially a distance A. In other words, movable and stationary contact comb teeth  210  and  212  have a substantially uniform gap A between their opposing vertical surfaces. In this embodiment, movable contact comb teeth  210  may have a smaller cross-section than stationary contact comb teeth  212  so the movable contact comb teeth may flex to contact the stationary contact comb teeth substantially along their length. 
     At the end of second contact spoke  254 , movable contact comb teeth  262  extend from a tangent member  264  to the spoke. Movable contact comb teeth  262  are interdigitated in-plane with stationary contact comb teeth  266  extending from a stationary contact pad  268 , which is located above substrate  203 . In one embodiment, adjacent movable and stationary contact comb teeth  262  and  266  are parallel and the shortest distance between them is substantially distance A. In other words, movable and stationary contact comb teeth  262  and  266  have a substantially uniform gap A between their opposing vertical surfaces. In this embodiment, movable contact comb teeth  262  may have a smaller cross-section than stationary contact comb teeth  266  so the movable contact comb teeth may flex to contact the stationary contact comb teeth substantially along their length. 
     At the end of actuator spoke  254 , movable actuator comb teeth  216  extend out from opposite sides of a tangent member  270  to the spoke. Movable actuator comb teeth  216  are interdigitated in-plane with stationary actuator comb teeth  218  extending from a stationary actuator pad  220 , which is located above substrate  203 . Together movable and stationary actuator comb teeth  216  and  218  form an actuator for rotating body  202 . In one embodiment, adjacent movable and stationary actuator comb teeth  216  and  218  are parallel and the shortest distance between them is substantially distance B, which is larger than distance A. In other words, movable and stationary actuator comb teeth  216  and  218  have a substantially uniform gap B between their opposing vertical surfaces. In this embodiment, inherent asymmetry in movable and stationary actuator comb teeth  216  and  218  allows the actuator to rotate body  202  in one direction with electrostatic force when they experience a voltage/electrical potential difference as shown in  FIG. 2B . Inherent asymmetry is introduced by the manufacturing process of switch  200 . In other embodiments, intentional asymmetry is introduced by design to control the rotational direction of body  202 . For example, each movable actuator comb tooth  216  may have substantially uniform gap B with an adjacent stationary actuator comb tooth  218  on its left side and a larger substantially uniform gap C with an adjacent stationary actuator comb tooth  218  on its right side to rotate body  202  in a clockwise direction as shown in  FIG. 2B . 
     Stationary contact pad  214  may serve as or be coupled to a source terminal of switch  200 , stationary contact pad  268  may serve as or be coupled to a drain terminal of the switch, and stationary actuator pad  220  may serve as or be coupled to a gate terminal of the switch. The role of stationary contact pads  214  and  268  may be reversed. The voltage/electrical potential difference between movable actuator comb teeth  216  and stationary actuator comb teeth  218  may be provided by a voltage source  224  supplying gate voltage/electrical potential Vg directly or indirectly to stationary actuator pad  220 , and another voltage source supplying a bias voltage/electrical potential directly or indirectly to a stationary spring pad  206 . In one embodiment, stationary spring pad  206  is coupled to stationary contact pad  268 , which directly or indirectly receives drain voltage/electrical potential Vd from a voltage source  226 . In another embodiment, stationary spring pad  206  is coupled to stationary contact pad  214 , which directly or indirectly receives source voltage/electrical potential Vs from a voltage source  228 . In yet another embodiment, stationary spring pad  206  is floated to an arbitrary voltage/electrical potential different from gate voltage/electrical potential Vd. Voltage sources  224  may represent circuitry separate from switch  100  in a larger device, such as a phase shifter, a smart antenna, a cell phone, or a switchable filter. Voltage sources  226  and  228  may represent circuitry downstream and upstream from switch  200  in the larger device. 
     When movable actuator comb teeth  216  and stationary actuator comb teeth  218  rotate hub  258 , movable and stationary contact comb teeth  210  and  212  come into contact, as well as movable and stationary contact comb teeth  262  and  266 , to close a circuit from one switch terminal to the other (e.g., from pad  214  to pad  268 ). Voltage source  228  may supply source voltage/electrical potential Vs to stationary contact pad  214  to create a current from the source terminal to the drain terminal. 
       FIG. 3  illustrates a MEMS electrical switch  300  in an off state in one or more embodiments of the present disclosure. Switch  300  is a variation of switch  200  and can be made using typical semiconductor manufacturing processes. 
     In switch  300 , a hub  302  consists of two electrically insulated halves  302 A and  302 B held together by an insulator  304  (shown in phantom), such as silicon oxide, so the hub rotates as one unit. Hub halves  302 A and  304 B may have interlocking features, such as intertwined fingers, and insulator  304  may be formed between the interlocking features as well as on top or below other portions of the hub halves. Hub half  302 A is connected to contact spokes  252  and  254 , and by a spring  204 A to a stationary spring pad  206 A. Hub half  302 B is connected to actuator spoke  256 , and by springs  204 B and  204 C to stationary spring pads  206 B and  206 C, respectively. 
     As before, voltage source  224  provides gate voltage/electrical potential Vg to stationary actuator comb teeth  218 . However, in one embodiment, stationary spring pad  206 B or  206 C is coupled to stationary contact pad  268 , which directly or indirectly receives drain voltage/electrical potential Vd from voltage source  226 . In another embodiment, stationary spring pad  206 B or  206 C is coupled to stationary contact pad  214 , which directly or indirectly receives source voltage/electrical potential Vs from voltage source  228 . In yet another embodiment, stationary spring pad  206 B or  206 C is floated to an arbitrary voltage/electrical potential different from gate voltage/electrical potential Vg. As hub halves  302 A and  302 B are electrically insulated from each other, any current loss that may result from contact pad  214  to spring pad  206  in  FIG. 2B  is avoided. The same concept may be applied to switch  100  in  FIGS. 1A and 1B  to separate body  102  into two insulated halves. 
     Various other adaptations and combinations of features of the embodiments disclosed are within the scope of the invention. For example in the above switches, the stationary contact comb teeth may be angled so the movable contact comb teeth become parallel to the stationary contact comb teeth when they contact as the body rotates. During the off state of the switch, the shortest distance from a tip of each stationary contact comb tooth to a movable contact comb tooth on one side would be about distance A so the contact comb teeth would touch before the actuator comb teeth. Numerous embodiments are encompassed by the following claims.