• Proposal 542: Advanced On-Wafer Mixer Chip Evaluation and Screening for ALMA Superconducting Mixers

  • Reviewer 5

Grade: 5

ADVANCED ON-WAFER MIXER CHIP EVALUATION AND SCREENING FOR ALMA SUPERCONDUCTING MIXERS

1. Alignment with NA ALMA Partnership strategic goals;

Most ALMA receivers rely on SIS mixers. This study will improve screening methods for the microfabricated chips, radically reducing development time and cost of future development efforts. The development of this test infrastructure will support multiple strategic goals by reducing the cost of SIS mixer device development. In particular, such screening infrastructure is critical to multi-pixel receiver development.

2. Strength of the scientific case for the proposed ALMA upgrade concept; Comment on the relevance to the ALMA 2030 development documents.

This upgrade will significantly reduce the man-hours required for screening and testing of SIS mixer chips. While this doesn’t address any specific science case, it impacts any that require upgrading and maintaining SIS mixers.

3. Quality of the upgrade conceptual design;

Good. The crucial component of maintaining low-temperatures at the device during probing has been achieved. This study builds upon this technology to enable the introduction of this screening method into the ALMA device development path.

A clear design is presented for automating the probing of the system as well as the control software.

One design concern not discussed is that of the closed-cycle cooler upgrade. One can assume it is a commercially available upgrade, but the thermal lift of the closed cycle cooler could be significantly less than that of a liquid cooled system. A short discussion comparing the expected thermal loading to the heat lift of the closed cycle refrigerator at 4K would improve this proposal.

4. Readiness for production in the context of the ALMA Development Plan (the aim is to support a range of upgrades including both those which can be implemented rapidly and those requiring longer-term research and development);

By the end of this project an automated cryogenic probe station should be ready for SIS mixer development.

5. Strength of the consortium organization (if applicable);

N/A

6. Qualifications of the key personnel of the Study;

Excellent. Professor Lichtenberger and his team at UVa has many years of experience developing superconducting mixers. In addition, they have unique experience developing probes for high-frequency circuits.

7. Technical expertise, past experience (also in series production, if relevant) and technical facilities in the Institutes taking part in the Study;

Excellent. UVa is the source of Band 3 & 6 SIS mixer devices and the sole source in North America for SIS devices in general.

8. Assessment of the level of risk inherent in the design;

Low. The primary challenge of wafer-level probing at 4K has already been demonstrated. This proposal is focused on refining the infrastructure so that it can be introduced into the production line.

9. Strength of the Scientific Team supporting the Study;

N/A

10. Level of support guaranteed by the Institutes;

Acceptable.

11. Budgeted cost of the Study;

The costing seems appropriate. There is an additional value addition by the institution contributing 50% of the closed-cycle cooler conversion.

  • Reviewer 7

Title of ALMADev Proposal: "Advanced On-wafer Mixer Chip Evaluation and Screening for ALMA Superconducting Mixers" by Lichtenberger et al.

Review Comments

The proposal seeks to develop a new automated cryogenic probe station for SIS junctions at UVML. This cryogenic probe station will use a closed-cycle refrigerator and precision 3-axis micro-controller based positioners for probe placement. Such a test station would significantly speed up the time it takes currently to test wafers and SIS junctions.

The science case for the proposal is driven simply by the fact that UVML is the single most important foundry for SIS mixers in the US, and that the continued supply of reliable and tested SIS junctions relies on a test setup that needs to be automated. The current testing procedure is entirely too manual and time consuming. By avoiding consumable cryogens this proposal also aims to cut the cost of evaluation of SIS junctions.

The current procedure for evaluation of SIS mixers involves mounting a SIS device on a carrier chip and dip-testing in a liquid helium dewar. The proposers have an existing cryogenics test station partially built by Lakeshore Cryotronics, but modified with custom probes. One of the issues with this probe is that the DUT never gets cold enough. The proposers will fabricate a second generation probe with adequate thermal isolation to get the DUT cold enough.

The assembled team has worked together well to produce a test station with better probes than supplied with Lakeshore. The scope of the work is well covered by the resources invested in the project. The proposed automated test station will positively impact all devices being built for most ALMA bands.

Not enough explanation is given to the interfaces between the external 3-axis micro-controller and the motion inside the cold cryostat. What feedback mechanisms are available to judge position with respect to test wafer? Some discussion on Z-position is provided. But remediation of position errors or errors in placement of probe with respect to mask is never discussed.

Very little discussion is included on the choice of the closed-cycle refrigerator. Will the design use the Lakeshore cryostat? What about the mechanical linkages between the cryostat and the refrigerator? Details are not provided to gauge how much work is involved in converting to a closed-cycle system.

The study is well aligned with ALMA's long term goals.

Review Score: 4.5

  • Reviewer 10

Superconducting Mixers Arthur Lichtenberger

Score 8

The goal of this proposal is basically to upgrade a cryogenic probe station at UVA in a number of ways to better position the PI to screen his SIS mixers. The probe station will be retrofitted to support a 4-K closed cycle cooler and various notional modifications to the system are proposed to reduce the environmental heat load. A recently developed DC probe will be further developed under the program and probe positioning will be automated. Finally, test wafers have been budgeted.

While it is certainly true that the PI is a leader in SIS mixers fabrication and such a system would better position him to deliver mixers, there are a number of significant weaknesses to the proposal. First of all, closed-cycle systems reaching 4 K are notoriously hard to implement. In fact, there is a large effort to build such a system going on at NIST, under IARPA funding. Another company (Microxact) has used two coldheads to do this (and still does not advertise functionality below 4.5K). It is not that it is impossible to reach 4K with a 1.5 K coldhead, it is just very hard to do so. The standard Lakeshore closed cycle system employs a 1.5 W 4.2 K coldhead and does not go below 5.5 K when two probe arms are mounted. Moreover, vision systems in Lakeshore probe stations are quite poor quality and even so, the illumination system used with their closed cycle system causes significant heating (for our system, covering the window causes a noticeable reduction in temperature). So, it is unclear how the PI would implement a vision system that is efficient enough to not load the cold head and heat up the system while at the same time providing a crisp enough image to enable automation. It is also not clear how an existing Lakeshore station would be modified to accommodate a cryocooler; the chuck is likely quite different and considerable work has gone into vibration isolation in the closed cycle systems. It seems more appropriate to just trade in the existing system for a closed cycle system (an option on Lakeshore’s website). The final concern has to do with the vision system that would be required to automate probing. These systems typically have a fixed chuck (the authors do not mention a mobile chuck) and as such, the camera would have to be mobile; this is not discussed.

  • Reviewer 11

Grade: 7

Title ADVANCED ON-WAFER MIXER CHIP EVALUATION AND SCREENING FOR ALMA SUPERCONDUCTING MIXERS

1. Alignment with NA ALMA Partnership strategic goals; This proposal is tangentially related to the strategic goals by increasing the efficiency and lowering the cost of testing SIS mixers. While this is an important goal eventually, it is not clear from the proposal if there is sufficient mixer production throughput to justify this particular proposal. (goal 2.1)

2. Strength of the scientific case for the proposed ALMA upgrade concept; Comment on the relevance to the ‘ALMA 2030’ development documents. No particular science case is given. Certainly if all the mixers for one or more bands in the array are upgraded it would presumably be done with some science case in mind (and as part of the ALMA 2030 development). For such an endeavor, the proposed test infrastructure would be invaluable, but it’s not clear what science case this proposal would benefit presently.

3. Quality of the upgrade conceptual design; The design of the test setup is based on proven technologies and is well thought out.

4. Readiness for production in the context of the ALMA Development Plan (the aim is to support a range of upgrades including both those which can be implemented rapidly and those requiring longer-term research and development); It seems that this test infrastructure could be rolled out on a short timescale. In particular, by the end of the proposed project, the testing system would be up and running, ready to test full wafers of SIS mixers.

5. Strength of the consortium organization (if applicable); N/A

6. Qualifications of the key personnel of the Study; The personnel are world leaders in SIS development and testing.

7. Technical expertise, past experience (also in series production, if relevant) and technical facilities in the Institutes taking part in the Study; UVML is the premier US lab fabricating and testing SIS mixers and have all the relevant facilities and experience needed.

8. Assessment of the level of risk inherent in the design; Very low risk

9. Strength of the Scientific Team supporting the Study; N/A

10. Level of support guaranteed by the Institutes; Substantial support, in particular significant in-kind contribution

11. Budgeted cost of the Study; Seems adequate.

  • Reviewer 13

Grade: 0.1

Title: Advanced on-wafer mixer chip evaluation and screening for ALMA superconducting mixers

1. Alignment with NA ALMA Partnership strategic goals; Comment: This proposal is well-aligned with ALMA NA strategic goals in that the proposed work would better facilitate testing of superconducting mixer chips required for future ALMA receiver upgrades.

2. Strength of the scientific case for the proposed ALMA upgrade concept; Comment on the relevance to the ‘ALMA 2030’ development documents. Comment: In that any future upgrade to enhance ALMA sensitivity, be it interns of bandwidth, noise, or number of receiver pixels, requires replacement SIS mixers; this proposal has strategic value in all science cases connected to the ALMA band 6.

3. Quality of the upgrade conceptual design; Comment: The proposed activity is technically sound and the likelihood of success is high.

4. Readiness for production in the context of the ALMA Development Plan (the aim is to support a range of upgrades including both those which can be implemented rapidly and those requiring longer-term research and development); Comment: The proposed work would significantly shorten turn-around time for superconducting mixer chip fabrication and testing, therefore better enabling receiver developments in ALMA band 6.

5. Strength of the consortium organization (if applicable); Comment:

6. Qualifications of the key personnel of the Study; Comment: Dr. Lichtenberger and his group at UVA have a long history of providing superconducting mixer chips to the US community, principally to NRAO, and are well-qualified to oversee and perform the proposed tasks.

7. Technical expertise, past experience (also in series production, if relevant) and technical facilities in the Institutes taking part in the Study; Comment: Lichtenberger’s group has the required expertise, have made production runs of ALMA Band 6 mixers, and the clean-room facilities at UVA are excellent.

8. Assessment of the level of risk inherent in the design; Comment: This is a low-risk proposal.

9. Strength of the Scientific Team supporting the Study; Comment: There is little in the way of inherent scientific staff supporting this proposal. However, the proposed work is clearly worthy of support, since the impact of significantly enhancing the future development and production of quality mixer chips for ALMA Band 6 is obvious.

10. Level of support guaranteed by the Institutes; Comment: The proposal states that half of the cost of the refrigerator conversion (approximately $67,000) will be borne by other internal UVA funding outside of this proposal and outside of NRAO. This amounts to ~ 20% of the total cost of the upgrades proposed here.

11. Budgeted cost of the Study; Comment: The proposed cost estimates seem reasonable and consistent with the proposed work.

-- AlWootten - 2017-07-18
Topic revision: r2 - 2017-07-18, AlWootten
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