Although there are capacitive surface micromachined force sensors with adequate resolution for cell manipulation and microneedle injections, it comes with the sacrifice of dynamic range and linearity. In contrast, optical based force sensors can provide the desired resolution and maintain relatively large sensing ranges compared to similar capacitive sensors. Plus, optical interferometry provides a sensing method that uncouples the conflicting design parameters, such as sensitivity and linearity. The current drawback to optical interferometry is the large off-chip equipment that is currently used in the operation of optical sensors. However, innovative techniques are being applied to surface micromachined microphones that allow off-chip components to be integrated onto the sensing chip. These same techniques can easily translate to the force sensor presented in this research, due to the similarities in the sensing methods. The thrust of this work is to explore a mechanism approach for enhancing the performance of a surface micromachined optical force sensor. A new design is presented which introduces a special mechanism, known as the Robert’s mechanism, as an alternate means in which the device is structurally supported. The new design’s implementation is achievable using an equivalent compliant mechanism. Initially, an analytical set of pseudo-rigid-body-model equations were developed to model the compliant design. A more accurate model was then constructed using FEA methods. The geometric parameters of the compliant Robert’s mechanism were then optimized to obtain a sensor with improved linearity and sensitivity. Overall, the force sensor provides higher sensitivity, larger dynamic range and higher linearity compared to a similar optical force sensor that uses a simple structural supporting scheme. In summary, this paper demonstrates the effectiveness of using a mechanism approach for enhancing the performance of MEMS sensors. The expected impact is to improve biomedical experiments and help further advance research that can improve quality of life.

One of the challenges facing microrobotic manufacturing is the ability to sense interactions for force-guided assembly of small devices. There is a need for a force transducer with the ability to sense forces in multiple degrees-of-freedom in the mN range with resolution on the order of 10 µN for microassembly applications. This paper presents theoretical studies for developing a surface micromachined piezoresistive force transducer that can measure normal force in the zdirection and moments about the x and y-axes. The devices proposed here are based on a compliant platform design with integrated piezoresistive sensing elements fabricated in a modified SUMMiT process. Various configurations and sensor element layouts are explored to determine the relationship of the applied forces and moments experienced during assembly and the corresponding strain. Structural and finite element analysis is used to determine the elastic response of the device and establish the best locations and orientations of the sensing elements to effectively utilize the piezoresistive effect of the polysilicon sensors. Initial experiments show the polysilicon piezoresistors to have a gauge factor of approximately 25. The expected sensitivities for these devices are presented.

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