High frequency operation of Josephson vortex flow transistor with a controlled damping

Both HTS and LTS junctions, respectively YBaCuO grain boundary junctions made on MgO 24/spl deg/ [001] tilted bicrystals and shunted Nb/AlOx-Al/Nb "SNOP" tunnel junctions deposited on sapphire have been used in asymmetrically biased Josephson vortex flow transistors (JVFT). As shown previously by Gross et al. (1995), we verify that the self field effect induced by current bias in asymmetrically designed JVFT with large screening parameter /spl beta//sub L/ can be used for increasing the current gain. Gain of about 10 up to 77 K are obtained with practical YBaCuO devices. High frequency operation of the devices has been experimentally verified up to the MHz range and extrapolated to GHz by using the control input gate coupled in a coplanar configuration to the vortex flow SQUID array, while reasonable values of transresistance, bandwidth and dynamical range are observed. Influence of the damping on the JVFT performances has been also studies experimentally by varying the subgap resistance of the Nb tunnel junctions. Amplifiers made of asymmetrical HTS JVFT may be competitive with SQUID or FET amplifiers for NMR, Electromagnetic Compatibility or Infrared imaging applications.