Zhimin Zhou

The evaluation of Young's modulus and residual stress of nickel films by microbridge testings

The variation of deflection and maximum stress of a nickel film microbridge with load was investigated over a wide range of length, thickness, elastic modulus and residual stress by both large and small deflection theories of microbridge testings. The limits of deflection and load for a microbridge to be deformed elastically were determined by the assumption that the maximum stress could not be more than the yield strength. Furthermore, the deflection and load limits of small deflection theory were decided by setting a threshold beforehand for the normalized deflection and maximum stress difference between large and small deflection theories. Based on the results above, the dimensions of the nickel microbridge samples were chosen and the deflection range suitable for the small deflection theory was calculated. The nickel film microbridge samples electroplated on a Si(100) substrate were fabricated by MEMS and the microbridge testings were conducted with a load and displacement sensing nanoindenter system. From small deflection theory, the Youngs modulus and residual stress for the electroplated nickel films were calculated and the results were 190.5 GPa and 86.6 MPa, respectively.

Fabrication of 3D MEMS toroidal microinductor for high temperature application

Based on Microelectromechanical systems (MEMS) technique and thick photoresist lithography technology, a new toroidal-type inductor for high temperature application has been successfully developed. In the fabrication process, heat-resistant materials are used, alumina as insulator and supporting materials instead of polyimide, heat resistant glass for underlay instead of normal glass, and copper for coil. The maximum inductance is 87nH at 0.826GHz and maximum of quality factor (Q-factor) is 4.63 at 0.786GHz, at room temperature. With simulation of thermal deformation, it shows that the developed toroidal inductor can be suitable for high temperature application, from 300 to 700^oC.

Transverse, longitudinal and perpendicular giant magnetoimpedance effects in a compact multiturn meander NiFe/Cu/NiFe trilayer film sensor

A compact multiturn meander NiFe/Cu/NiFe trilayer film giant magnetoimpedance (GMI) sensor, with the width of 100 µm for NiFe film and 60 µm for Cu film, the space of 40 µm and a turn number of 10 is fabricated by the MEMS technique on a silicon substrate. The transverse, longitudinal and perpendicular GMI effects are respectively investigated in the magnetic field range of 0–120 Oe and the frequency range of 1–40 MHz. With the magnetic field it could be up to 86.6% for the transverse GMI effect at 15 MHz and 120 Oe, 166% for the longitudinal GMI effect at 15 MHz and 20 Oe and 165% for the perpendicular GMI effect at 10 MHz and 50 Oe. In addition, there are platform stages, which correspond to the magnetic field range of 0–20 Oe for the transverse GMI effect and 0–10 Oe for the perpendicular GMI effect. Furthermore, the peak of GMI effects covers a large frequency range, which could be up to about several tens of MHz. The GMI platform and the strong GMI effect could be attributed to the demagnetization effect and enhanced electromagnetic coupling from the compact meander sensor structure, respectively. The broad frequency peak originates from the different magnetization process in the straight segment in the meander structure.

The evaluation of Young's modulus and residual stress of Cu films by NiFe/Cu bilayer film microbridge tests

This paper proposes a method to estimate the thickness limit for single-layer microbridge tests and also the thickness limit of one film on another film with known thickness for bilayer microbridge tests. To evaluate the mechanical properties of the Cu film, which could not be measured by single-layer microbridge tests, the NiFe single-layer film and NiFe/Cu bilayer film on silicon substrate are fabricated onto the microbridge by the MEMS technique. A load–deflection experiment is conducted upon the ceramic shaft adhered to the microbridge center by means of the XP nanoindenter system. From single-layer microbridge theory, Youngs modulus and the residual stress of the NiFe film are deduced to be 192.74 ± 8.10 GPa and 287.75 ± 16.18 MPa, respectively. The data are introduced into bilayer microbridge theory and Youngs modulus and the residual stress of the copper film are calculated to be 118.71 ± 6.54 GPa and 41.34 ± 4.42 MPa, respectively. The experimental results correspond well with those of nanoindentation.

Residual strain of a Cr film characterized by micromachined beams

Microbridge samples of length 134–368 µm and width 20 µm, composed of a Cr film of 150 nm thickness sputter-deposited on a silicon substrate, were fabricated by the MEMS (microelectromechanical systems) technique. The profile of buckled beams was measured by the white light interference technique and only the middle and the boundary of the beams are shown in the results. From the length and amplitude, the full profile of the beams was fitted and residual strain in the film was deduced. The fitted results correspond well with the experimental results and the residual strain is about 5.826 × 10−3.