An automated measurement system for cryogenic wafer probing is described. The system has been designed for up to four simultaneous broadband on-chip measurements in the temperature range from 4 to 300 K. Special requirements for superconducting samples have been taken into consideration. Most of the measurements needed for characterization of superconducting thin films and circuits can be done with a high degree of precision in the low- and high-frequency region. Details of the design are presented and the system performance is discussed.
An automated measurement system for cryogenic wafer probing is described. The system has been designed for up to four simultaneous broadband on-chip measurements in the temperature range from 4 to 300 K. Special requirements for superconducting samples have been taken into consideration. Most of the measurements needed for characterization of superconducting thin films and circuits can be done with a high degree of precision in the low- and high-frequency region. Details of the design are presented and the system performance is discussed.
Robust maturation of cryogenic electronics has been limited by the lack of high-throughput measurement capabilities, especially for electronics that operate at 4 K. Automated on-wafer probing to characterize the dc and RF performance of components and complete circuits has been a critical element in the development of room temperature electronics. We report here the development of a fully automated wafer prober that operates with the wafer cooled to a temperature of 4 K and has the ability to null the ambient magnetic field to below 100 nT, which is important for measuring superconducting circuits with the wafer prober.
An on-wafer measurement technique allowing measurement of a superconducting film's penetration depth without post device-fabrication separation of the chips has been investigated. Coplanar waveguide (CPW) probes and a CPW to microstrip transition are utilized, allowing the use of commercially available LakeShore® CPX-1.5K cryogenic CPW probing station capable of microwave measurements to 50 GHz. The use of CPW probes allows for rapid prototyping and is nondestructive to the device wafers, and hence compatible with many device fabrication technologies. Measurement techniques utilizing resonant microwave circuits have been reported (1),(2), but require mounting to custom-made test fixtures and are not performed on-wafer, but instead on individual diced devices. However, such a dicing requirement is incompatible with our ultra-thin Si, Au beam-lead chip architecture (3). In addition to a traditional resonant circuit measurement technique, a technique that uses on-wafer calibration standards is discussed. The on-wafer calibration eliminates possible effects introduced by the testing setup and potentially offers additional advantages such as a size reduction and a direct measurement of RF loss. The designs and results for both measurement techniques are reported for NbTiN films.
Coulomb blockade thermometers (CBTs) have attracted more interest in recent years, as the demand for sub-one Kelvin thermometry has increased, especially due to the prevalence of dilution refrigerators in research and applications in quantum technology. CBTs can be operated both as a primary thermometer, requiring no prior calibration, or as a simple resistance thermometer in the secondary mode after calibration. As new scalable fabrication processes for quantum devices and cryogenic electronics are being developed, cryogenic wafer characterization methods must also scale up to provide statistical data on device parameters. Currently, characterization throughput of cryogenic devices is limited by the turnover time and sample capacity of traditional cryostats, where a measurement cycle for only a few devices can take several days. In this work, we demonstrate wafer-scale cryogenic characterization of a recently developed TiW/Al-AlOx/TiW normal-metal tunnel junction technology using CBTs. Measurements performed in a 300 mm cryogenic wafer prober (CWP) show on-chip electron temperatures below 700 mK across a full 150 mm wafer, as determined by primary thermometry. These results establish wafer-level testing below 1 K as a viable approach for large-scale cryogenic characterization of electrical devices, opening a pathway toward high-throughput screening of quantum devices and direct wafer-scale characterization of aluminum-based superconducting circuits.
We present the RF characterization of 2-µm-wide superconducting coplanar waveguides made of 100-nm-thick niobium (Nb) or niobium nitride (NbN) films fabricated on 200 mm silicon wafers. Measurements of the two-ports S-parameters up to 25 GHz in a 4.7K–14 K temperature range with an added direct current up to 115 mA were done using a cryogenic probe station. With proper RF calibration and de-embedding procedure, both temperature and dc current dependence of the RF superconducting properties are analyzed. We report a kinetic inductance of 0.15 pH/□, a critical current density of 50 MA/cm2, and a critical temperature of 8.9 K for Nb as well as 4.27 pH/□, 3 MA/cm2, and 13.8 K for NbN. A telegraphist transmission line model taking into account the BCS theory has been developed and the comparison with the measurements is discussed.
Integrated semiconductor circuits operating at cryogenic temperatures can play a crucial role in scaling quantum computing architectures based on trapped-ion and superconducting qubits. Other technologies, such as low-temperature detectors, can also benefit significantly from these circuits. These applications demand high-frequency, cryogenic temperature measurement systems for the thorough characterization of semiconductor components and circuits. This work presents a customizable, high-frequency, fast, and reliable cryogenic measurement setup for measurement temperatures ranging from room temperature to 4.2 K. It features up to two dc probes or two ground-signal-ground probes for frequencies of up to 67 GHz, which can be configured in a 180° or 90° configuration. In addition, up to 48 BeCu wires configured as twisted pairs provide supply and control signals. Furthermore, up to four rf connections can be mounted directly to a printed circuit board. The setup features an optical microscope in the vacuum chamber to position the probes, which is further utilized by a machine vision algorithm, allowing the detection of pads and automatic positioning of the probes over the pads. The hardware is located in a 550 × 500 × 500 mm3 large vacuum chamber with two independent pulse tube cryocoolers with cooling powers of up to 0.9 and 0.4 W at 4.2 K. Exemplary room temperature and cryogenic S-parameter, transient frequency (fT), time-domain, capacitance-voltage, and dc measurements of single transistors and integrated circuits fabricated by Infineon are presented, demonstrating the system's measurement capability for quantum computing and other applications.
We have developed a cryogenic probe and cryostat system to test both active and passive superconducting devices and circuits up to microwave frequencies at variable temperatures. Our system consists of two basic parts: the cryostat and the matching probe. The cryostat is a unique, very efficient, variable temperature, flow-type cryostat, where we control temperature without electrical heaters. It is magnetically shielded and allows rapid testing between 4.2 K and room temperature. Probes developed for this cryostat have a larger number of shorter cables than standard dip-type probes. They are designed to test chips or chip assemblies without additional packaging. Chips or chip assemblies can be quickly mounted and dismounted from a fixed spring-contact assembly. Each probe has 56 wide-bandwidth signal cables. We have repeatedly used these probes for testing both active and passive superconducting integrated circuits up to 20 GHz. The probe and cryostat combination provides a testing capability that is simultaneously high frequency, dc magnetic shielded, has variable cryogenic temperature, and quick turnaround.