High--$T_c$ RF SQUIDs with Large Inductance of Quantization Loop

Experimental data on signal and noise characteristics of high–$T_c$ RF SQUIDs with large inductance of quantization loop are presented. The SQUIDs were produced by a thick–film HTS–technique of painting on the Y${}_2$BaCuO${}_5$ substrate. For the first time, a steady quantum interference was observed in RF SQUID with the inductance as large as $L_S=6.6$ nH, that is, 60 times higher than the fluctuation inductance $L_F\simeq {10}^{-10}H$ at the liquid nitrogen temperature T=77 K. A new method is offered to evaluate the sensitivity of RF SQUID with optimum inductance of the quantization loop.