積體式高溫超導交流量子干涉元件製作及其特性研究

Abstract

The superconducting quantum interference device (SQUID) is one of the important applications of high-TC superconductors. Since the high sensitivity to magnetic fields, the SQUID magnetometers have been used in many researches on weak field detections. They have been widely used in non-destructive evaluation (NDE), scanning SQUID microscope (SSM), magnetocardiology (MCG), magnetoencephalography (MEG), and low field nuclear magnetic resonance (NMR). Most of the high-TC SQUID magnetometers in use are dc SQUIDs. The dc SQUID has two Josephson junctions in a superconducting ring. In an rf SQUID, there is only one Josephson junction. The signal of the rf SQUID is read out by a copper loop inductively coupled to the SQUID through a LC resonant circuit. A great improvement of high-TC rf SQUIDs was done by Zhang et al. in Jülich Research Center, Germany. They have developed many kinds of high-TC rf SQUIDs. The flux concentrator further improves the effective area of the magnetometer. The noise level can be as lower as that of high-TC dc SQUIDs. Recently, they used a substrate resonator which cause the SQUID more stable and to be set up more simply. In this work, I try to study the noise characteristics of the high-TC rf SQUID magnetometers. A new designed rf SQUID magnetometer is developed. The principle of rf SQUID and the development of high-TC rf SQUID magnetometer are introduced in chapter 1 The preparations of the flux concentrator and the rf SQUID are in chapter 2. Measuring procedures including the resonant frequency, the effective area and the noise spectral density are also in this chapter. Chapter 3 shows variations of the effective area and resonant frequency due to changing the size of the superconducting flux concentrator. The flux noise of the high-TC rf SQUID magnetometer is resonant-frequency-dependent. The experiment results are fitted by Chesca’s formula. In chapter 4, we developed a new design which is called an integrated rf SQUID magnetometer. The rf SQUID is fabricated directly onto the SrTiO3 substrate resonator. The same concept is used to design a integrated 1st order planar gradiometer in chapter 5.