SWCam 2014 Log
January 29 SWCam Telecon – first joint A/R, electronics, and SWCam telecon
Gordon, Scott, Mike, Steve, Ganesh, German, Justin, Reinhold, Jason, Jordon, Hiro, Brian, Darren, Attila,
Matt B., Thomas, Chris
Gordon made an overall statement about MSIP being due on March 12. Last detector updates need to
be done by March 5 or so. Also would like positive words about the A/R coating progress for that March
5 date.
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Detectors
o Darren worried about whether or not another fabrication run will be done by 5 weeks
from now
 Darren says aiming for CSO run in the spring – 350 um only
o Chris – working on understanding fundamental principles of detectors
 Flat transmission curve: created new card with parallel inductor
 Now starts at 50 to 250MHz with roll-off above 450 MHz
 Just used off the shelf components in a warm pc card
 Attila working on chirp readout
 Working on dual polarization and lenslet arrays
 Sent out lenslets for A/R coating – they were lost, and a new one is
being made for free
 Plan is to do response tests with uncoated lenses and then with coated
lenses
o Matt. – notes that we need good low frequency noise performance down to 1/10 Hz for
large scale sky measurements
 This is not yet done, it is suggested that Chris could put together time streams
and someone else might due the FT for the noise
o Attila – the chirp readout drives resonators to bifurcation. Plan on improving the
dynamic range – currently 5 to 10 dB below bifurcation, which is too tight a constraint.
A/R coating issues
o A new DRIE sample is constructed and will be sent to Colorado when they are ready
o New parylene sample is being prepared – the accuracy of the layer thickness that can be
delivered is in question - Both DRIE and paralyne samples are 1” silicon squares, 1 mm thick
 Darren speculates one could coat a large area, and then trim it down for testing
so that the coating is more likely uniform
o Jordan reports that the Colorado cryostat is now reconfigured, and ready for testing of
SWCam 350/450 µm pieces
February 5 SWCam Telecon
Gordon, German, Steve, Ganesh, Thomas, Justin, Mike, Jack, Matt, Joe, Darren
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A/R coating issues
o 6 wafers w/ 3 different hole sizes sent to Colorado today (42.83, 42.83, 44.83 µm)
o Depth is suspected to be 50 to 64 µm which is not right.
o Pato and Galen are working on wafer bonding, and depositing oxide layers onto a wafer
o There is an issue with tracking wafers – some confusion on which one is which.
Detectors
o Matt B. reports that there are issues with the latest TiN LEKIDS. Q’s for devices
manufactured after July have degraded over time to about 104 now.
 Might be related to deposition with a different Ti target.
 Pre-sputter should remove any contamination.
 Should get answer soon
o Darren TiN problem is worrisome.
 Dual polarization device is not yet fabricated, so this could derail the schedule
 There was also a bit of work required on the cold-head that slowed things down.
Readouts
o Atilla tested chirp readout.
 A short timescale steam appears to work
 Has excited some resonances up to adequate levels for readout
 Readout levels sufficient for BLIP
o Ganesh
 Roach box now in his possession, is buying computer/server for Roach system
that will also serve for the data reduction pipeline.
 Custom board report from Ryan is that required IC’s from 4 channel custom
board from JPL…
Software
o Thomas reports that SolidWorks PDM is approved by management
Lenses
o Steve is refining the costs for the silicon lenses. Newtec quote exists today
o Two other companies are interested
February 12 SWCam Telecon
Ganesh, Pato, Steve, Gordon, German, Brian, Mike, Jason, Jordan, Reinhold, Jack, Matt, Hiro, Darren
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A/R coating issues
o Jason – cryostat working, measured a bunch of samples
 Non-linear response – will attack by increased filtering to lower signals
o Jordan – have 1 sided paralyne sample
 Shooting for 51 µm thickness, but it came out at 45 µm
o Darren asks about communication with Teltech. Has the double sided sample arrived?
o Fringes appear, but there is at least a week of work before ND filters are in place to
enable a good measurement
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Can’t cut down BP too much with filtration since the fringing off the ½ mm thick
piece is pretty severe.
o Samples were damaged in shipment – needs improvement
o The DRIE pieces were not properly labeled and therefore mixed up
o German – showed some predictions – Jason says the qualitatively the measurements
look like the predictions in German’s plots
 German says curvature in the bottom of a pill-box is not a big effect
o Pato talks about wafer bonding
 Anneal to attach at 1000 -1200 C for 2 hours in N2 atmosphere, or for weeks
at ~300C
 Makes oxygen bond. Needs no pressure
 Works for 6” wafers in a Class 1000 clean room.
 Really want a Class 10 clean room, as dust is an issue with bubbles in the bond
 Would also work on SiN
 Mean thickness is 1.030 4.8 µm – not clear how much is from wafer, and how
much of this variance is the bond.
 Preparation for bonding is cleaning in base, then acid – 2 sides are polished
Detector issues
o Darren speaking for Chris – debugging of TiN deposition process.
 Good news is that the higher Q’s are restored
o Current run of optical tests involve gradient index lenslets with parylene A/R coatings
o Velt laser cut lenslets next up on the testing block.
February 19 SWCam Telecon
Attending: Gordon, Brian, German, Ganesh, Steve, Thomas, Justin, Matt Bradford, Hiro, Jordan
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Jordan: nonlinearity of FTS is an issue.
o Cut aperture, added a filter to cut bandwidth.
o Working on a compromise between non-linearity and signal strength
o Double coated parylene is now at Colorado – transmission appears to peak near 1 THz
o May want to measure these samples with a profilometer
o Brian will ship them 3 different gell packs with the new wafers to be tested today.
Matt Bradford reports good news on MAKO pixel testing.
o Parylene coated with gradient index lenses are showing BLIP performance between 290
and 150 K
o They haven’t done a nitrogen load yet, but so far, NEP  loading – not limited by TLS
noise
Meeting was short, since Jonas was giving a SOFIA talk on KIDs at the same time.
February 26 SWCam Telecon
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Attendees: Jordan, German, Thomas, Ganesh, Pato, Steve, Hiro, Matt B., Darren, Attila, Chris
Jordan
o Shows FTS measurements of A/R coated silicon that have tmax ~ 100 to 120%, and ~
20%
o Modulation in signal is issue with non-linearity. It is recommended that he add an
absorber and turn down BB source
German
o DRIE should have 50 µm pitch
 Calculates widths of 44.83, 42.83, 40.5 µm
 39.85 µm  630 GHz
 41.7 µm  680 GHz
 44.67 µm  800 GHz
 Hole size changes, but depth doesn’t (=63.4 µm)
 The 44.67 µm hole has a reflection minimum at 800 GHz, but is non-optimal for
800 GHz work since the pitch and depth are not optimally matched
Pato – Reviews profilometer measurement technique
o The observed cut rate (µm/loop) is variable, and likely stochastic so we will need to
monitor all the time
o This variation is likely due to variations in plasma density
o The final depth needs to be within 1.7 µm of the design goal
o Gordon mentions the need for cost estimates, but we need to get true tolerance first
Attila – Chirp readout review
o Need readout noise BLIP
o Extract spectrum from 125 to 260 MHz at chirp rate of 2-4 KHz
o 100,000 channels read out at this 2-4 kHz so that we can extract positions of
resonances
o He is now getting reasonable frequency noise – levels are comparable to those of
previous readouts on the CSO with MAKO
o Going to work on the data for the next week or two, and then prepare a proper
presentation (ACTION)
o Issue is that we are close to saturation of the ADC
o Tone readout vs. chirp readout
 Readout noise is range/noise  need to maximize readout range in ADC
o Could probably crank up the gain 10 dB more
o Ganesh asks if 12 bit ADC is adequate? Answer: Yes
Chris – detectors
o It is clear the current generation of arrays is photon noise limited at 300 K. There is still
evidence for photon noise at 150 K
o Optical efficiency is a bit low – 30 to 40%
o These are currently single polarization devices
 He is getting ready to fab new dual polarization device
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 This device could be tested in as soon as two weeks (REPORT)
There is still no backshort, and lens spot-size is bigger than the absorber
 Gordon comments: this might explain much of the lost optical efficiency – Chris
agrees
Order of fabrication is:
 dual polarization – next couple of weeks
 backshort – immediately following
Hopes to have dual pole, backshort, lenslet array at CSO in spring
Steve asks about 850/2mm plan: answer 850 in lab during summer
March 5 SWCam Telecon
Attendees: Jordan, German, Thomas, Ganesh, Pato, Steve, Hiro, Jack
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Jordan reports improvements in FTS data
 Taking data with BB temp turned down a factor of two, chopping faster (to keep
the average bolometer temp more constant)
 Gets lower SNR but better linearity
 Discovering issues with humidity in their N2 purged chamber
 Has tested both 2 sided and single sided parylene but not ready to show the
data; Cornell DRIE samples next up on his testing schedule.
 FTS calibrated with silicon blanks.
o Pato presented talk on bonding exercise
 7 cm2 bubble appears in ½ mm thick, 4” diameter wafer bonded to silicon flat
 Difficult to make the bond. Need to climb a ladder to insert silicon pieces into
oven. Bond occurs at 1200 C – in paper they use 800 C after annealing at 100
to 200 C for 2 weeks to let gases escape.
o Brian reports on slumping
 Plan is to slump first on SiC to test process
 Ring is used to push surface down onto lenses after SiC test.
 He notes that the bond is a chemical bond (Si:O:Si), not a molecular bond. OH is
formed on surface in a bath. During bonding, H2O evolves and needs to escape.
o [ACTION] Parylene process: how well is thickness controlled? Can German address
this?
Electronics
o Layout of latest version (JPL /Ryan Monroe’s Custom version 1) is produced.
o First board due in May/June
o Debugging expected to be finished by August at which point Cornell can get a few
boards fabricated for testing here.
o This version should be done between September and the end of the year.