Electrical generator or motor structure – Non-dynamoelectric – Thermal or pyromagnetic
Reexamination Certificate
2000-04-05
2001-10-30
Dougherty, Thomas M. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Thermal or pyromagnetic
C310S307000
Reexamination Certificate
active
06310419
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to microelectronic devices, and more particularly to microelectronic resistor arrays and methods for fabricating the same.
BACKGROUND OF THE INVENTION
Resistor arrays are used for a variety of applications including digital potentiometers. Such arrays may be generated from discrete resistors or from commercially available integrated circuits including a plurality of resistors. The resistors are typically coupled with electrical relays or switches, such as dual in-line package (DIP) switches, to provide a selectable range of resistance values. Furthermore, controllable switches rather than manual switches may be utilized to provide control over the selection of the resistor values to a processor or other control device, typically digitally. Such a digital potentiometer may be useful, for example, in instrument setup, tuning, calibration or wherever a resistor value needs to be changed remotely in a circuit. However, combining metal to metal contact switches with discrete resistors, while generally providing high isolation and low insertion losses, typically requires significant circuit board space as compared with integrated circuit type devices.
Microelectromechanical systems (MEMS) have been developed as alternatives to conventional electromechanical devices, such as relays, actuators, valves and sensors. MEMS devices are potentially low-cost devices, due to the use of microelectronic fabrication techniques. New functionality also may be provided, because MEMS devices can be much smaller than conventional electromechanical devices.
It has been proposed to utilize particular MEMS devices integrated with a variety of other electrical components. U.S. Pat. No. 5,880,921 to Tham et al. is directed to a monolithically integrated switched capacitor bank using MEMS technology. U.S. Pat. No. 5,834,975 to Bartlett et al. discusses an integrated, variable gain microwave frequency power amplifier which includes a number of individual amplifier stages having outputs connected to MEMS switches. U.S. Pat. No. 5,872,489 to Chang et al. is directed to an integrated, tunable inductance network with a number of fixed inductors fabricated on a common substrate along with a switching network including MEMS switches. Similarly, it is known to provide a resistor array in combination with MEMS switches. Notwithstanding the above-described advances and suggestions, there continues to be a need for selectable resistor networks having a small footprint and suited to large scale production.
SUMMARY OF THE INVENTION
The present invention provides resistor networks, digital potentiometers and microelectromechanical structures that include a plurality of resistors selectable by a plurality of microelectromechanical actuators. More particularly, a thermal relay type of actuator is provided as a switch which may selectively control which of the plurality of resistors is connected. The heater for the thermal relay and the plurality of resistors may be formed from a common layer of the integrated circuit structure, such as a doped polysilicon layer, which may simplify the manufacturing process. Preferably, a thermal arched beam actuator, for example as described in U.S. Pat. No. 5,909,078, is utilized in combination with film resistors to provide an integrated circuit device suitable for applications such as digital potentiometers.
In embodiments of the present invention, the integrated circuit resistor network includes a plurality of resistors and a plurality of switches, each of the switches being electrically coupled in series with an associated one of the plurality of resistors. The resistor network further includes a plurality of microelectromechanical actuators, each of the microelectromechanical actuators being coupled to one of the plurality of switches, and a controller electrically coupled to the plurality of microelectromechanical actuators that selectively activates at least one of the plurality of microelectromechanical actuators to toggle the associated one of the switches coupled to the at least one of the plurality of microelectromechanical actuators. In one embodiment, the microelectromechanical actuators are thermal relays including a heater element comprising a region of a resistive material on an integrated circuit substrate and the plurality of resistors are film resistors each comprising a region of the resistive material on the integrated circuit substrate. The resistive material is preferably polysilicon and more preferably the resistors are thin film doped polysilicon resistors.
In further embodiments, respective ones of the plurality of resistors have a resistance value stepped by a factor of two from another of the plurality of resistors. Preferably, each of the plurality of resistors provides a set of associated resistance values stepped by factors of two from a base resistance value. The base resistance value may be between about 20 ohms and about 300 ohms. Each of the doped polysilicon film resistors may include a number of resistor squares of a polysilicon sheet having a sheet resistance value (rho) so as to provide a desired resistance value. In one embodiment, at least one of the plurality of resistors includes a plurality of matched polysilicon resistor elements.
In other embodiments of the present invention, the microelectromechanical actuators are thermal relays including an integrated circuit substrate and spaced apart supports on the integrated circuit substrate. A beam extends between the spaced apart supports that expands upon application of heat thereto to thereby cause displacement of the beam between the spaced apart supports. In one embodiment, the integrated circuit substrate defines a reference plane and the beam is an arched beam which extends between the spaced apart supports and which expands upon application of heat thereto for movement parallel to the reference plane defined by the integrated circuit substrate. The thermal relays may further include a heater disposed on the integrated circuit substrate so as to underlie the arched beam and to be spaced apart from the arched beam. The heater may be adapted to heat the ambient surrounding the arched beam which, in turn, heats the arched beam to cause further arching of the beam as a result of thermal expansion thereof, to thereby cause displacement of the arched beam parallel to the reference plane defined by the integrated circuit substrate.
In further embodiments, the controller is coupled to the heater of each of the thermal relays to initiate heating of the arched beams so as to activate the corresponding one of the plurality of microelectromechanical actuators. The controller may output a select pulse that generates a current flow to activate the at least one of the plurality of microelectromechanical actuators. The resistor network may further include a latch circuit that maintains the activated at least one of the plurality of microelectromechanical actuators in an activated position. In one embodiment, the latch circuit outputs an electrostatic holding voltage that maintains the activated at least one of the plurality of microelectromechanical actuators in the activated position. The latch circuit may include a capacitor associated with each of the plurality of microelectromechanical actuators and the controller may have a plurality of latch outputs each of which is electrically coupled to one of the capacitors that initiates charging of the associated one of the capacitors to thereby output the electrostatic holding voltage.
In further embodiments of the present invention, a digital potentiometer integrated on an integrated circuit substrate is provided including a plurality of film resistors on the integrated circuit substrate and a plurality of microrelay switches on the integrated circuit substrate. A respective resistor and switch are coupled between first and second reference terminals of the digital potentiometer. A control circuit selectively activates one of the plurality of microrelay switches to provide a desired resistance between the first and
Dougherty Thomas M.
JDS Uniphase Inc.
Myers Bigel & Sibley & Sajovec
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