Insulator layer based mems devices

Abstract

The present invention relates to using an insulator layer between two metal layers of a semiconductor die to provide a micro-electromechanical systems (MEMS) device, such as an ohmic MEMS switch or a capacitive MEMS switch. In an ohmic MEMS switch, the insulator layer may be used to reduce metal undercutting during fabrication, to prevent electrical shorting of a MEMS actuator to a MEMS cantilever, or both. In a capacitive MEMS switch, the insulator layer may be used as a capacitive dielectric between capacitive plates, which are provided by the two metal layers. A fixed capacitive element may be provided by the insulator layer between the two metal layers. In one embodiment of the present invention, an ohmic MEMS switch, a capacitive MEMS switch, a fixed capacitive element, or any combination thereof may be integrated into a single semiconductor die.

What is claimed is: 
     
         1 . A semiconductor die comprising:
 a substrate;   a micro-electromechanical system (MEMS) device comprising:
 a fixed capacitive plate formed by a first metallization layer over the substrate; 
 a movable capacitive plate formed by a second metallization layer that is suspended over the fixed capacitive plate; and 
 an insulator layer formed between the fixed capacitive plate and the movable capacitive plate; 
   wherein the moveable capacitive plate is configured to move toward the fixed capacitive plate upon actuation of the MEMS device and the insulator layer is positioned to prevent the movable capacitive plate from contacting the fixed capacitive plate such that the MEMS device has a first capacitance upon actuation of the MEMS device.   
     
     
         2 . The semiconductor die of  claim 1  wherein the fixed capacitive plate is a combined actuator and capacitive plate. 
     
     
         3 . The semiconductor die of  claim 1  further comprising an actuator formed by the first metallization layer over the substrate, wherein the actuator is formed separately from the fixed capacitive plate. 
     
     
         4 . The semiconductor die of  claim 3  wherein the insulator layer is further formed between the actuator and the movable capacitive plate such that the insulator layer is positioned to prevent the movable capacitive plate from contacting the actuator. 
     
     
         5 . The semiconductor die of  claim 1  wherein the MEMS device has a second capacitance when the MEMS device is not actuated. 
     
     
         6 . The semiconductor die of  claim 5  wherein the first capacitance is greater than the second capacitance. 
     
     
         7 . The semiconductor die of  claim 1  further comprising:
 a first terminal; 
 a second terminal; 
 wherein the MEMS device is configured to present the first capacitance between the first terminal and the second terminal upon actuation of the MEMS device. 
 
     
     
         8 . The semiconductor die of  claim 7  wherein the MEMS device has a second capacitance when the MEMS device is not actuated, the second capacitance being presented between the first terminal and the second terminal. 
     
     
         9 . The semiconductor die of  claim 7  wherein:
 the first terminal is electrically coupled to the fixed capacitive plate and is configured to receive an actuation signal that is operable to actuate the MEMS device. 
 
     
     
         10 . The semiconductor die of  claim 7  further comprising an actuator formed by the first metallization layer over the substrate and a control terminal electrically coupled to the actuator, wherein:
 the actuator is formed separately from the fixed capacitive plate; 
 the control terminal is configured to receive an actuation signal that is operable to actuate the MEMS device; and 
 the insulator layer is further formed between the actuator and the movable capacitive plate such that the insulator layer is positioned to prevent the movable capacitive plate from contacting the actuator. 
 
     
     
         11 . The semiconductor die of  claim 10  wherein the MEMS device has a second capacitance when the MEMS device is not actuated, the second capacitance being presented between the first terminal and the second terminal. 
     
     
         12 . The semiconductor die of  claim 11  wherein the first capacitance is greater than the second capacitance. 
     
     
         13 . The semiconductor die of  claim 1  wherein the insulator layer is formed from a capacitive dielectric. 
     
     
         14 . The semiconductor die of  claim 13  wherein the capacitive dielectric is selected from a group consisting of Silicon Nitride, Silicon Dioxide, and Aluminum Oxide. 
     
     
         15 . The semiconductor die of  claim 1  further comprising a second insulating layer formed over the substrate, wherein the first metallization layer is formed over the second insulating layer. 
     
     
         16 . The semiconductor die of  claim 1  wherein the substrate is a semiconductor substrate. 
     
     
         17 . The semiconductor die of  claim 16  wherein the semiconductor substrate is formed from Silicon. 
     
     
         18 . A method of manufacturing a micro-electromechanical systems (MEMS) device comprising:
 providing a semiconductor substrate;   forming a fixed capacitive plate over the semiconductor substrate;   forming an insulator layer over the fixed capacitive plate; and   forming a movable capacitive plate over the insulating layer such that the movable capacitive plate is suspended over the fixed capacitive plate.   
     
     
         19 . The method of  claim 18  wherein the fixed capacitive plate is formed as an actuator of the MEMS device. 
     
     
         20 . The method of  claim 18  further comprising forming an actuator that is separate from the fixed capacitive plate.