Active solid-state devices (e.g. – transistors – solid-state diode – Responsive to non-electrical signal
Reexamination Certificate
1999-07-08
2001-07-17
Mintel, William (Department: 2811)
Active solid-state devices (e.g., transistors, solid-state diode
Responsive to non-electrical signal
C257S415000, C200S0830SA, C200S0830SA, C335S078000, C335S080000, C361S819000, C438S050000
Reexamination Certificate
active
06262463
ABSTRACT:
FIELD OF USE
The present invention relates to a micro-machined switch (micro-switch) and a micro-machined sensor (micro-sensor) which performs mechanical switching or signaling in response to an externally applied acceleration force. This invention also relates to techniques for fabricating such a micro-switch or micro-sensor.
BACKGROUND ART
Many industrial applications require force-actuated mechanical switches. Such mechanical switches provide reliable isolation when in an open state, and provide a low resistance electrical path when in a closed state. However, conventional force-actuated mechanical switches are relatively large and have relatively slow switching speeds. Moreover, conventional force-actuated mechanical switches are typically difficult and costly to fabricate. In addition, it may be difficult to control the sensitivity of force-actuated mechanical switches.
One application of a force-actuated mechanical switch is as a safety switch to avoid accidental deployment of air bags (i.e., air bag switches). In this case, the air bag switch is mounted in an automobile. The air bag switch remains in an open state when the external force applied to the air bag switch is less than a threshold, which is usually, characterized in g's. (A “g” is defined as a force resulting from an acceleration of 9.8 meters/second
2
.) When the external force applied to the air bag switch is greater than a predetermined threshold (e.g., when the automobile is in a head on collision) the air bag switch is forced into a closed state, thereby allowing deployment of the air bag.
Force-activated mechanical switches or sensors are also used as shock sensors in computer disk drives. In the case of rigid disk drives, when the mechanical shock or vibration imposed by the environment is excessive, the drive electronics must be able to detect such a disturbance and turn off the read/write circuits in order to avoid overwrite errors. Conventional shock sensors typically use a cantilever beam, which deflects in the presence of external forces. These shock sensors sense the deflection by means of stress imposed on laminated piezopolymeric films or piezoresistive strain gages. Alternatively, these shock sensors can sense the deflection by monitoring the changes in capacitance between the beam and the ground plane.
Similarly, in many other applications, it is desirable to have an analog sensor that outputs a continuous signal proportional to acceleration.
It would therefore be desirable to have a force-activated mechanical switch or sensor which has reliable sensitivity, durability, fatigue and deformation characteristics, has accurate (or linear) operating characteristics, and which can be fabricated at low cost and with batch manufacturing processes.
SUMMARY
Accordingly, the present invention provides a micro-switch and micro-sensor that use a monocrystalline material, such as monocrystalline silicon, as the structural material. Monocrystalline silicon has advantageous stiffness, durability, fatigue and deformation characteristics. The silicon is moved by externally applied forces to provide an electrical connection between contact elements or to output an analog signal.
In one embodiment, the micro-sensor includes an upper structural member and a lower structural member. The lower structural member includes a substrate and one or more planar coils are fabricated on the upper surface of the lower structural member. The substrate can be, for example, a semiconductor material such as monocrystalline silicon.
The upper structural member includes a monocrystalline substrate. The monocrystalline substrate can be, for example, a semiconductor material such as monocrystalline silicon. The monocrystalline substrate is fabricated to form a frame, a platform that is laterally surrounded by the frame, and a plurality of spring elements, which flexibly connect the frame to the platform. In a particular embodiment, the spring elements have a serpentine shape. The monocrystalline substrate has a planar lower surface, and a pole tip is located on the lower surface of the platform portion of the substrate.
The upper structural member is connected to the lower structural member to form the micro-sensor. More specifically, the frame of the upper structural member is connected to the lower structural member. As a result, the pole tip is suspended over the coil of the lower structural member. When an external force is applied to the resulting structure, the spring elements flex to allow the platform to move toward the lower structural member. When the external force becomes sufficiently large, the platform will deflect to move the pole tip into the planar coil. The thickness and geometry of the platform and spring elements can be selected to provide the desired operating characteristics for the micro-sensor. The pole tip can be made of a ferromagnetic material or a permanent magnetic material. A ferromagnetic pole tip will change the measured inductance of the coil as the pole tip moves in the coil. A permanent magnetic pole tip will induce a voltage in the coil as the pole tip moves in the coil. The inductance or voltage of the coil is therefore monitored to determine whether the pole tip, and therefore the platform, is moving in response to an external force.
In another embodiment, a micro-switch includes a lower structural member and an upper structural member. The lower structural member includes a substrate, a plurality of electrically conductive contact pads located on the upper surface of the substrate, and a plurality of raised spacer pads formed on the upper surface of the substrate. The substrate can be, for example, a semiconductor material such as monocrystalline silicon.
In this embodiment, the upper structural member includes a monocrystalline substrate having a planar lower surface, and an electrically conductive bridge contact pad located on the lower surface of the substrate. The monocrystalline substrate can be, for example, a semiconductor material such as monocrystalline silicon. The monocrystalline substrate is fabricated to form a frame, a platform that is laterally surrounded by the frame, and a plurality of spring elements, which flexibly connect the frame to the platform. In a particular embodiment, the spring elements have a serpentine shape. In one embodiment, the frame and platform have a thickness of approximately 500 &mgr;m, while the spring elements have a thickness of approximately 6 &mgr;m.
The upper structural member is connected to the lower structural member to form the micro-switch. More specifically, the frame of the upper structural member is connected to the raised spacer pads of the lower structural member. As a result, the bridge contact pad is suspended over the contact pads of the lower structural member. The spacing between the bridge contact pad and the contact pads of the lower structural member are determined by the height of the spacer pads formed on the lower structural member.
When an external force is applied to the resulting structure, the spring elements flex to allow the platform to move toward the lower structural member. When the external force becomes sufficiently large, the platform will deflect to move the bridge contact pad into electrical contact with the contact pads of the lower structural member. The thickness and geometry of the platform and spring elements can be selected to provide the desired operating characteristics for the micro-switch.
The present invention will be more fully understood in light of the following detailed description taken together with the drawings.
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Miu Denny K.
Tang Weilong
Bever Hoffman & Harms LLP
Hoffman E. Eric
Integrated Micromachines, Inc.
Mintel William
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