Electricity: magnetically operated switches – magnets – and electr – Electromagnetically actuated switches – Polarity-responsive
Reexamination Certificate
2002-04-01
2004-04-13
Donovan, Lincoln (Department: 2832)
Electricity: magnetically operated switches, magnets, and electr
Electromagnetically actuated switches
Polarity-responsive
C200S181000
Reexamination Certificate
active
06720851
ABSTRACT:
TECHNICAL FIELD
The invention concerns micro electromechanical switches and more particularly micro electromechanical switch circuits.
BACKGROUND
Micro electromechanical switches are used in a variety of applications up to the microwave frequency range. A micro electromechanical switch is usually a beam with support at one or both ends. The support will normally either extend above a substrate surface or be level with the substrate surface, i.e. a micro electromechanical switch is normally built on top of the substrate surface or into the substrate. The beam acts as one plate of a parallel-plate capacitor. A voltage, known as an actuation voltage, is applied between the beam and an actuation electrode, the other plate, on the switch base. In the switch-closing phase, or ON-state, for a normally open switch, the actuation voltage exerts an electrostatic force of attraction on the beam large enough to overcome the stiffness of the beam. As a result of the electrostatic force of attraction, the beam deflects and makes a connection with a contact electrode on the switch base, closing the switch. When the actuation voltage is removed, the beam will return to its natural state, breaking its connection with the contact electrode and opening the switch. Important parameters of micro electromechanical switches are their sensitivity to an actuation voltage and their transient time. A short transient time (high switching frequency) will result in a very high actuation voltage and vice versa since they, at least in part, depend on the same physical properties of the switch. There is room for improvement in the control of micro electromechanical switches.
SUMMARY
An object of the invention is to define a manner to control the transient time of micro electromechanical switches.
Another object of the invention is to define a manner to control the sensitivity of micro electromechanical switches.
A further object of the invention is to define a manner of controlling at least one physical characteristic of micro electromechanical switches on which at least one of either a sensitivity or a transient time of micro electromechanical switches depend.
A still further object of the invention is to define a micro electromechanical switch which is resilient to externally induced mechanical influences.
The aforementioned objects are achieved according to the invention by changing the characteristics of micro electromechanical switches by applying a control signal which either changes one or more parameters of the micro electromechanical switches or which controls beam movement by feedback signals. It is thereby possible to change switching transient time, maximum switching frequency, power tolerance, and/or sensitivity (actuation voltage) of a micro electromechanical switch.
The aforementioned objects are also achieved according to the invention by a micro electromechanical switching structure. The structure comprises a switching element which in turn comprises a first switching support, a switching actuator control electrode, and a switching beam having a first end and a second end, the first end of the switching beam being supported by the first switching support. According to the invention the micro electromechanical switching structure further comprises a first reconfiguration support, a first reconfiguration beam and a first reconfiguration actuator control electrode. The first reconfiguration support is spaced apart from the first switching support. The first reconfiguration beam comprises a first end and a second end. The first end of the first reconfiguration beam is supported by the first reconfiguration support and the second end of the first reconfiguration beam is supported by the first switching support. The first reconfiguration actuator control electrode is arranged between the first reconfiguration support and the first switching support. Further according to the invention the first switching support is ductile, suitably horizontally ductile, to thereby enable transfer to the switching beam of tension variations of the first reconfiguration beam caused by actuation of the first reconfiguration beam by means of the first reconfiguration actuator control electrode, which actuation thereby changes characteristics of the switching element.
Preferably the first reconfiguration support is an anchor, i.e a rigid support being more or less uninfluenced by created tensions. In some applications the switching element further comprises a second switching support, the second end of the switching beam is then supported by the second switching support. Suitably the second switching support is also of an anchor type. Also in some applications the micro electromechanical switching structure further comprises a second reconfiguration support, a second reconfiguration beam and a second reconfiguration actuator control electrode. The second reconfiguration support is spaced apart from the second switching support. The second reconfiguration beam comprises a first end and a second end. The first end of the second reconfiguration beam is supported by the second reconfiguration support and the second end of the first reconfiguration beam is supported by the second switching support. The second reconfiguration actuator control electrode is arranged between the second reconfiguration support and the second switching support. The second switching support is also ductile, suitably horizontally ductile, to thereby enable transfer of tension variations of the second reconfiguration beam caused by actuation of the second reconfiguration beam by means of the second reconfiguration actuator control electrode, to the switching beam. The second reconfiguration support can be an anchor.
The aforementioned objects are also achieved according to the invention by a micro electromechanical switching arrangement comprising a switching element. The switching element comprises a first support, an actuator control electrode, and a switching beam having a first end and a second end. The first end of the switching beam is supported by the first support. According to the invention the micro electromechanical switching arrangement further comprises a switching beam position measurement device and an actuator control signal unit. The switching beam position measurement device generates a beam position signal related to a position of the switching beam in relation to a position of the actuator control electrode. The actuator control signal unit generates an actuator control signal in dependence on the beam position signal and a desired switching beam position signal, the actuator control signal being coupled to the actuator control electrode. In some applications the switching element further comprises a second support, the second end of the switching beam is then supported by the second support. Preferably the switching beam position measurement device utilizes capacitive measurement methods for generating the beam position signal. Suitably the switching beam position measurement device comprises a variable capacitance element and a Wheatstone bridge in which the variable capacitive device is one element.
By providing a micro electromechanical switching circuit according to the invention a plurality of advantages over prior art micro electromechanical switching circuit are obtained. Primary purposes of the invention are to make flexible micro electromechanical switches with variable/changeable characteristics. This will enable higher production yields, the switches can be trimmed after production to desired specifications, and/or the switches can be used in a broader variety of applications with either different requirements on the specifications and/or requirements of changeable specifications/characteristics. MEMS switches according to the invention are also more resilient to external mechanical influences, such as vibrations etc., i.e. a knock on the MEMS switch will not cause the beam of the switch to vibrate uncontrollably, but instead any such external mechanical disturbances will be dampened either by the beam gap control loo
Carlsson Erik
Hallbjörner Paul
Donovan Lincoln
Nixon & Vanderhye P.C.
Telefonaktiebolaget LM Ericsson (publ)
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