A series array of DC SQUIDs

A series array of 100 DC SQUIDs has been fabricated using trilayer Nb-AlO/sub x/-Nb junctions. The SQUIDs are modulated with a common flux bias line and produce an output voltage swing of several millivolts across the array. The large output voltage will allow direct connection to room temperature electronics without the transformer coupling and resulting frequency limitations commonly associated with DC SQUID amplifiers. A bandwidth of DC to at least 175 MHz for a 100-SQUID array has been measured. The series array will be used as the output stage for a multistage integrated SQUID amplifier.