Highly Sensitive Coplanar Line Thin-Film Sensor Using SrTiO Film

A very sensitive thin-film sensor was developed using a coplanar line fabricated from SrTiO (Sr₃₃Ti₁₆O₅₁) film (0.5, 1, 2, 3, and 6 $\mu $ m thick), amorphous CoNbZr film (5 $\mu $ m thick), and Cu/Cr film (4 $\mu $ m/0.2 $\mu $ m). The deposited SrTiO film had high permittivity of around 31. This film enhanced the sensitivity of the magnetic field sensor, a phase change of more than 100°/Oe and gain of over −40 dB being achieved simultaneously. The sensor with SrTiO film enhanced the sensitivity about 1.6 times greater than that with SiO₂ film because of the high permittivity of the SrTiO film. The sensitivity of the sensor increased with increasing thickness of the SrTiO film, a thickness of around 3 $\mu $ m being sufficient for enhancement of the sensitivity.

I. Introduction

Biomagnetic measurement, such as in magnetocardiography (MCG) and magnetoencephalography is performed by SQUID [1], [2] or a laser-pumped magnetometer [3]. However, these sensors are very expensive and difficult to operate. On the other hand, while an induction coil [4] and a fluxgate sensor [5] are not so expensive, they are comparatively large in scale, making it difficult to integrate them in a sensor array. Highly sensitive thin-film sensors operating at room temperature are potentially applicable for biomedical or nondestructive evaluation. Thus, development of a magnetic thin-film sensor for measurement of biomagnetic signals at room temperature was the aim of this paper.