Effect of Pecvd Deposited Sio2 Interlayer on the Performance of Asic Integrated Anisotropic Magnetoresistance Sensors

Abstract

The sensitivity and accuracy of the anisotropic magnetoresistance sensors are heavily affected by the sensor architecture and material properties, such as the composition, thickness of the ferromagnetic film, the rate/method of the deposition, thermal treatment process. Nevertheless, for the new generation of anisotropic magnetoresistance sensors incorporated with application-specific integrated circuits, the introduced additional factors strongly influence the performance of the devices. In this paper, we fabricated NiFe Wheatstone bridge anisotropic magnetoresistance position sensor on an application-specific integrated circuits chip, which uses a layer of SiO2 as passivation. We show that the sensitivity of anisotropic magnetoresistance sensors strongly depends on the way of SiO2 preparation and post-annealing of the devices. The sensors fabricated on the thermally grown SiO2 performed stably with thermal annealing or introducing a TaN buffer layer between the SiO2 and NiFe film. A typical sensitivity obtained on these devices is 0.6~0.8 Gauss/mV; While, for the devices made on PECVD-SiO2 passivated integrated circuit chip, the device has a sensitivity 1.039 Gauss/mV before annealing and decreased to 0.298 Gauss/mV after annealing at 450℃. After introducing a TaN buffer layer, no such reduction is observed, and the device sensitivity is approximately 0.68 Gauss/mV. MOKE measurement shows that the sensitivity variation is mainly caused by a change of anisotropy field. We propose that the increased anisotropy field is resulted from the magnetostatic energy caused by a granular magnetic film surface.

Keywords: anisotropic magnetoresistance, ASIC incorporated sensor, TaN buffer, SiO2 deposition