Multi-Stage Integrated Direct-Current SUID Array Amplifiers

Superconducting Quantum Interference Devices (SQUIDs) are extremely sensitive detectors of magnetic flux and can be used as low noise amplifiers for many applications such as cryogenic detectors and biomagnetic measurements. In order to utilize a SQUID as an amplifier, extensive peripheral electronics are required. Such room temperature electronics are very expensive, specially for space-qualified applications, and are responsible for a substantial portion of the cost of the commercial magnetometer systems. Therefore, it is highly advantageous to simplify the electronics required to operate SQUIDs. This project will lead to the development of an all thin-film SQUID array amplifier chip. The proposed DC SQUID amplifier integrates several (on the order of a hundred) DC SQUID gates with a high sensitivity analog SQUID magnetometer. Each chip, in addition to having a SQUID array coupled to an analog SQUID, will also have an integrated superconducting transformer to facilitate its interface to an external pick up coil. This scheme will eliminate the need for the most critical part of the peripheral electronics, that is, the low noise amplifiers, which, in practical systems, determines the noise floor of the systems. Such a system will be compact and cost effective, and requires ordinary support electronics. As a result of this effort, it will be possible to design and fabricate SQUID chips that will contain arrays of such SQUIDs for integration in magnetometer systems, thereby reducing the complexity of the room temperature electronics for such systems. Due to significant progress in superconducting electronics at HYPRES in recent months, we are actually proposing to design, fabricate and evaluate these SQUID array amplifier chips under this phase I program. The goal for the flux noise for such chips is less than 5XlO-6~o/~Hz when operated from 4.2 K down to milliKelvins.