[12p-N403-1~14] 11.5 Junction and circuit fabrication process, digital applications

▼ [12p-N403-5] Half-Flux-Quantum Toggle Flip Flops Based on π-π-π SQUIDs

〇Feng Li¹, Yuto Takeshita¹, Masayuki Higashi¹, Masamitsu Tanaka¹, Taor Yamashita¹, Akira Fujimaki¹ (1.Nagoya Univ.)

Keywords:HFQ, Half flux quantum, TFF

In this work, we fabricated and demonstrated a novel Half-Flux-Quantum (HFQ) Toggle Flip Flops (TFFs) made up with only π-junctions, in which one π-junction was used for a non-switching phase shifter with a critical current of 4I_c and the other two junctions act as the switching elements with critical currents of I_c. All the π-junctions are un-shunted and fabricated based on the Nb/Pd₈₉Ni₁₁/Al-AlO_x/Nb multilayer structure. We observed the π-phase shift in the dependence of I_c on the external magnetic field in π-π-π SQUIDs. Ground plane holes are utilized to increase the inductance per unit length. According to the simulation, the operating margin of the HFQ TFF is about ±20%. The measurement was done with high frequency pulse trains and the output voltage measured at 4.2 K is exactly half of the input voltage, indicating the correct divide-by-two operation up to 18 GHz.