Cryogenic Integrated Circuit For Superconducting Nanowire Single Photon Detector

Superconducting nanowire single photon detectors(SNSPDs)have showed many superior performances so far.However,it is generally operated in a strongly nonlinear mode where only one output signal is generated even if more than one photon is absorbed;many applications,e.g.,spectroscopy,communication,biological imaging,astronomical observation,and quantum information processing,still require detectors for resolving the incident photon numbers even detecting the spatial and temporal information.Therefore,developing SNSPD arrays to realize photon-number-resolving,time-resolving and space-resolving has become a major research trend.At present,researchers can already read out the singles of an 8 X 8 multi-element array and resolve the positions of incident photons in an integrated multiplexed way by using 16 coaxial lines and commercial RF amplifiers at room temperature.In addition,research on reading the singles of an 8 X 8 multi-element array in cryogenic environment with an SFQ circuit is also in progress.However,the integrated multiplexed readout will limit the scale of multi-element array eventually due to the number of coaxial lines and heat load;designing and fabricating an SFQ circuit is complicated,and it is inconvenient to use for the additional magnetic shielding.Series array of superconducting nanowires can be read in the conventional way,and can also resolve the photon positions by choosing specific shunt resistor.In this respect,it is more advantageous than the multi-element array.But when the number of pixels in series is large,a special cryogenic RF amplifier with high input impedance will be needed to distinguish the amplitude of pulses caused by different number of incident photons.To meet this demand of series array of superconducting nanowires,we designed and fabricated the cryogenic integrated RF amplifiers with high input impedance based on Tower Jazz's 0.18?m SiGe BiCMOS process.My work mainly revolves around two aspects,the first is how to ensure the amplifier based on SiGe HBT can work normally at 4.2 K,the second is how to use the 50? measurement system commonly used in RF band to characterize the amplifier with high input impedance and extract its scattering parameters.The research results are as follows,1.Built the experiment platform and measured the temperature characteristics of resistor,capacitor and inductor over a temperature range of 300 K to 4.2 K;measured the input and output characteristics of three kinds of SiGe HBTs at different temperature,one of which are fabricated by Tower Jazz's process and the other two types are commercial available,compared the results with related literatures,obtained the general rules of SiGe HBT's DC characteristics with the decrease of temperature,and analyzed the possible reasons for the different behaviors of SiGe HBTs at cryogenic environment;measured the relation between performance of proportional current source and temperature.These works provide an important technical guarantee for the design and optimization of cryogenic integrated RF amplifiers.2.By using current source instead of voltage source as the power supply,the initial single-ended structure cryogenic circuit with 50? input impedance achieves about 10 dB gain and 2 MHz?1 GHz bandwidth,and successfully reads out the pulse signal of SNSPD,which ensures the feasibility of the selected SiGe process.On this basis,participated in the design of single-ended and differential structure cryogenic integrated circuits with high input impedance.By making the quiescent point of the circuits adjustable,the challenge of lack of the models of related components at cryogenic environment is overcomed,which ensures the SiGe HBTs in the circuit can be biased properly at 4.2 K from the perspective of engineering,and can enable the circuit work normally.3.studied how to extract the characteristic parameters of RF amplifiers with high input impedance by using a vector network analyzer(VNA),analyzed the distribution ratio between the 50? RF test instruments and the device under test from the perspective of voltage transmission when their inpedances are mismatched,and proved that the gain of high input impedance amplifier obtained by the conventional 50?RF measurement system is 6 dB higher than its actual value.In addition,by contrasting the measured results obtained at different calibration position of VNA and simulating the input impedance of the circuit,clarified the influence of the long coaxial line on the measurement of impedance and gain of the circuit,which is used to connect the cryogenic and room temperature environment.The related work not only provides a technical reference for the measurement of high input impedance RF circuits,but also helps to deepen the understanding of how to analyze the coaxial lines when interconnecting the readout circuit with SNSPD.4.characterized the performance of single-ended and differential structure high input impedance RF amplifiers with VNA successfully.At room temperature,the measured results of these two types amplifiers match well with simulation.At 4.2 K,the single ended structure amplifier demonstrates 20 dB gain,3.8 MHz?1 GHz bandwidth,up to 6.7 k? input impedance and only 0.6 mW power dissipation,and the differential structure amplifier shows 26 dB gain,100 kHz?1 GHz bandwidth,up to 10 k? input impedance and 0.9 mW power dissipation.5.built and optimized the interconnection test system of cryogenic readout circuit and SNSPD,and make use of the two types cryogenic circuit read out the SNSPD's pulse signals successfully.The interconnection test system can not only monitor the circuit at low temperature to ensure that the circuit is in the normal working state,but also scan the ?-? curve of SNSPD,which can be used to determine the bias current of SNSPD and evaluate the influence of cryogenic circuit on the switching current of SNSPD.Such work laid a good foundation for the test of interconnection between cryogenic readout circuit and SNSPD in the future.