This paper presents the design, fabrication, and testing of a miniature latching accelerometer that does not require electrical power. Latching is attained by using a bistable compliant mechanism that switches from one mechanical position to another when the force on the accelerometer exceeds a threshold value. Accelerometers were fabricated by laser cutting the compliant mechanism switch out of both ABS and Delrin plastic sheets. Packaging consisted of gluing the single compliant layer to a supporting substrate. The switching thresholds of the accelerometers were varied from 10g to 800g by varying the surface area of the free moving section between 100 and 500 mm2.

https://iopscience.iop.org/article/10.1088/0964-1726/16/5/055/pdf

Plastic latching accelerometer based on bistable compliant mechanisms

A new micromechanism, the Spherical Bistable Micromechanism (SBM), is described. The SBM has several advantageous features, which include: two stable positions that require power only in transitioning from one to the other; robustness against small disturbances; and an output link with a stable out-of-plane orientation. The SBM may be useful in applications such as 2-D optical mirror arrays or in erecting out-of-plane structures.Copyright © 2006 by ASME

Spherical Bistable Micromechanism

The objective of this work is to demonstrate the feasibility of on-chip sensing of bistable mechanism state using the piezoresistive properties of polysilicon, thus eliminating the need for electrical contacts. Changes in position are detected by observing changes in resistance across the mechanism. Sensing the state of bistable mechanisms is critical for various applications, including high-acceleration sensing arrays and alternative forms of nonvolatile memory. A fully compliant bistable micro mechanism was designed, fabricated and tested to demonstrate the feasibility of this sensing technique. Testing results from two fabrication processes, SUMMiT IV and MUMPs, are presented. The SUMMiT mechanism was then integrated into various Wheatstone bridge configurations to investigate their potential advantages and to demonstrate various design layouts. Repeatable and detectable results were found with independent mechanisms and with those integrated into Wheatstone bridges.

/pdf/piezoresistive-sensing-of-bistable-micro-mechanism-state-4iyxa35ito.pdf

Piezoresistive sensing of bistable micro mechanism state

We propose a theoretical investigation of a new principle of bi-stable MEMS based on the remnant electrostatic force generated by the space-charge density that builds up when two semiconductors, having different doping densities, are brought into contact. Following a physical description of the device, a complete analytical formulation of some key parameters such as the pull-in and pull-out voltages could be obtained. The model reveals that both closed and open configurations of the switch MEMS can be stable states at zero applied voltage. The impact of the different technological parameters is also discussed in details, supporting that the so-called junction-MEMS might be an interesting alternative to address bi-stability in MEMS, still remaining fully compatible with the standard microelectronics technologies.

Principles of space-charge based bi-stable MEMS: The junction-MEMS

ORTHO-PLANAR MECHANISMS FOR MICROELECTROMECHANICAL SYSTEMS Craig P. Lusk Mechanical Engineering Doctor of Philosophy A method for representing the design space of ortho-planar mechanisms has been developed. The method is based on the Theorem of Equality of Orientation Set Measures (TEOSM) which allows mechanisms to be represented by points in an abstract space. The method is first developed for single loop planar folded mechanisms with revolute joints, and later extended to mechanisms with prismatic joints and to spherical folded mechanisms. Functions which assign a value to each point in design space can be used to describe classes of mechanisms and evaluate their utility for MEMS design. Additionally, this work introduces the use of spherical mechanisms in MEMS design. Spherical mechanisms have characteristics that may be useful in MEMS, including the capability of spatial positioning of a link and the ability to convert rotation about an axis perpendicular to the substrate to rotation about an axis parallel to the substrate. Spherical kinematics has been used to develop three novel mechanisms, the Micro HelicoKinematic Platform (MHKP), the Spherical Bistable Mechanism (SBM), and the Threedegree-of-freedom Platform (3DOFP). Mathematical models of these devices have been developed and MEMS prototypes have been designed and fabricated.

Ortho-Planar Mechanisms for Microelectromechanical Systems

Often microsystems require switches or mechanisms that can give two stable states. Currently, many micromechanical systems use a monostable switch to produce the two states: a first stable state when no power is applied and a second state that requires constant power to maintain the stability. Such a configuration is not efficient and consumes considerable electrical power during the 'on' state of the switch. A more efficient design would be a device that consumes energy only during the switching operation and does not consume any power while holding the stable states. Our novel micromechanical bistable switch design is based on the locking mechanism of an extension ladder. This switch was designed and fabricated through multi-user MEMS processes (MUMPs). Our paper outlines the design, simulation, animation and results from the testing of the micro-fabricated system. Actual performance of the switch was videographically analyzed and compared with theory and simulation.

S. Hu

Papers

A surface micromachined bistable switch