Towards a six degree-of-freedom resistive force sensor : device design and bonding technique

The design of a six degree-of-freedom force and moment sensor, using resistive read-out methods is presented in this thesis. An overview of resistive force sensors form the last two decades is given, in which key aspects in sensor design and measuring techniques are compared and discussed. Specific design requirements impose that the sensor should work in a force range higher then presented before in a multi-axis sensor. The design features a mechanical load reduction method, whereby the applied force is translated into a displacement to be measured by the sensing structures. Separate sensing structures for the normal and shear force are placed on the device in an array, enabling temperature compensation, differential measurement and a higher sensitivity. Eutectic bonding is proposed as the bonding technique for the sensor fabrication, allowing low-temperature processing and deposition of the strain gauges and bonding material in the same processing step. A study is presented into the research published about eutectic bonding and a summary is given of the scientific knowledge of this technique. Several experiments are conducted to find the optimal processing conditions and eutectic bond strength for various metal layer con- figurations. Results show various, never before published, fracture patterns and bond interfaces. Average bond strengths of up to 106 MPa are found, depending on the deposited metal layers. This work enables future development of a high-load resistive multi-axis force sensor and strong low-temperature wafer-to-wafer bonding.