Development of X-ray detection system by using an on-chip coil inetgrated superconducting tunnel junction

研制了一种用于高性能X射线探测器的片上线圈集成超导隧道结(OC^2-STJ)。OC^2-STJ由Nb基结和沉积在其上电极绝缘层上的超导微带线圈组成。微带线圈在结的绝缘层中产生磁场，以抑制约瑟夫森电流。制作的OC^2-STJ芯片被安装在带有55&gt；Fe X射线源的冷却舱中。冷却舱安装在紧凑型^3He-^4He稀释式制冷机的混合室中。在探测器运行期间，OC^2-STJ芯片在胶囊中保持恒温，以防止带状线圈电流馈线产生焦耳热。用电荷灵敏前置放大器收集入射X射线对激发的准粒子隧穿产生的电荷。为了降低输出信号中的噪声分量，将信号输入场效应晶体管(FET)通过弱热连接放置在冰箱的1K锅上。通过加热器将输入FET的温度调节到100K，以产生噪声等效电荷最小的输出电压脉冲。将FET温度控制在1K，使OC2-STJ芯片的温度保持在600mK左右。在OC2-STJ用于X射线探测的工作中，向微带线圈提供10~30 mA的电流。获得了OC^2-STJ芯片中敏感面积为10 0×10 0μm^2的菱形Nb基隧道结的响应特性。证明了OC^2-STJ在不使用普通外部电磁铁的情况下运行稳定。

An on-chip coil integrated superconducting tunnel junction (OC^2-STJ) was developed for high performance X-ray detector. The OC^2-STJ consists of a Nb-based junction and a superconducting microstrip coil deposited on the insulating layer deposited on the top electrode of the STJ. The microstrip coil generates the magnetic field in the insulating layer of the junction for suppression of Josephson current. The fabricated OC^2-STJ chip was mounted in a cooling capsule with the ^<55>Fe X-ray source. The cooling capsule was attached to the mixing chamber of a compact ^3He-^4He dilution refrigerator. The OC^2-STJ chip was held at a constant temperature in the capsule against the Joule heat generation in the current feed line of the strip coil during the detector operation. Electric charges produced by tunneling of excited quasiparticles by incident X-rays were collected by a charge sensitive preamplifier. To reduce noise components in the output signals, a field effect transistor (FET) of the signal input was placed on the 1 K pot of the refrigerator through a weak thermal link. The temperature of the input FET was regulated at 100 K by a heater to generate the output voltage pulses with the minimum noise equivalent charge. The temperature of the OC^2-STJ chip was kept around 600 mK with regulating the FET temperature at 1 K. In the operation of the OC^2-STJ for X-ray detection, the current from 10 to 30 mA was supplied to the microstrip coil. Response characteristics were obtained for a diamond-shaped Nb-based tunnel junction with a sensitive area of 100 × 100 μm^2 in the OC^2-STJ chip. A stable operation of the OC^2-STJ was demonstrated without using usual external electromagnets.