Development of a MEMS 3D Stress Sensor Using Strain Engineering for Out of Plane Stress Applications

  • Author / Creator
    Amr Adel Balbola
  • This work aims to enhance the performance of a MEMS-based 3D piezoresistive sensor, which has the capability of extracting the six temperature-compensated stress components. That sensor is made of an n-type piezoresistive element that has low pressure/out-of-plane piezoresistive (PR) coefficient, which causes low sensitivity for the out-of-plane normal stress measurement. Strain engineering is employed to improve the n-type sensing rosette sensitivity, since stretching the silicon lattice permanently reduces the atomic forces that interfere with the movement of electrons, which in turn affects the PR coefficients remarkably. Two approaches are adopted to integrate the strain technology with the sensing rosette. In the first approach, the ten-element rosette is fabricated onto biaxial pre-strained substrates to enhance its out-of-plane normal stress sensitivity. While the second technique exploits a local uniaxial stressor to devise a new 3D stress sensing rosette. This approach has the advantage of reducing the fabrication complexity and cost through avoiding n- and p-wells fabrication in the case of the dual polarity rosette and three n-wells for the single polarity chip. A full analytical study is carried out to verify the capability of the local strain approach to generate a set of linearly independent equations, which shows that the six stresses and temperature can be determined using the generalized equations. Both the biaxial and uniaxial strained chips are fabricated using surface microfabrication and fully calibrated using uniaxial, thermal, and hydrostatic loading. The preliminary
    calibration of the local strained chip proves its capability to extract the 3D stresses.
    The capability of the strained silicon-based 3D stress sensor to extract the out-of-plane stress is validated experimentally using a two-point shear bridge test. The tested chip captures the shear stress with 16 percent full-scale error, while the out-of-plane normal stress is extracted accurately using the developed chip with 11 percent error. As a consequence, the capability of the developed sensor to measure the out-of-plane stress is utilized to provide a low profile detector of the chip debonding. In other words, the significant correlation between the out-of-plane shear stress and the bonding stiffness is used to obtain a full picture of the chip adhesive deterioration in early phase. The same technique can be utilized to early detect the debonding in multilayer structures.

  • Subjects / Keywords
  • Graduation date
    Spring 2020
  • Type of Item
  • Degree
    Doctor of Philosophy
  • DOI
  • License
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