150 mm Si Detector Designs

All CAD designs can be found at /data/chocula/k100/CAD as well as on the lab's Windows Machine.

As of July 7th 2016, all items have been completed by the workshop and are ready to be assembled and tested. The following tasks were performed in the assembly:

1. Standard 1” DIBs sent from Matt Cherry at Stanford, were attached to the two electrode housings.
2. Both electrodes were clamped into place in their housings. 20 mil spacers were used on the LED side of both electrodes. On the source/bias/readout side, 10 mil spacers were used on the readout electrode, and 20 mil spacers were used on the HV electrode.
3. Two LED chips were attached to underside of each electrode and blue wire (type unknown) was soldered to connect DIBs and LED chips.
4. Small copper sheet was cut and folded to make two roughly 1cm x .5cm rectangles. A small hole was made in these rectangles for a 0-80 screw to pass through. A brass 0-80×5/32“ screw with a 0-80 brass nut and the one copper rectangle were screwed into the bias/readout screw hole on each electrode. The same blue wire was the soldered to the copper rectangle and the DIB.
5. The electrodes and crystal housings were stacked with top and bottom lids and secured with threaded rods produced earlier. Stack fit well together and was secured easily with rods.
6. Tried to mount the stack on a tower. We found that the bottom/crown lid inner diameter was too small to fit around the spool (it should have a diameter of 2.21”, but measured 2.18“). This must be sent to the shop to be fixed.
7. Switched bottom/crown lid with Hassan's housing crown lid (same design). We found that this did fit around the spool, however two screw holes connecting crown to spool were mangled. This must be sent to shop to re-tap. For now, we were able to secure stack with the four remaining holes. Bad holes were marked with an 'X' in capton tape.
8. Once tower and stack were assembled, we attempted to attach flexible side coaxes. We found that the flexible side coaxes were too short to connect to the furthest electrode, since this electrode's DIB is “upside down” compared to standard designs, and requires the flexible side coax be twisted to attach. We decided to instead to move the pins to the other side of each connector, such that the flexible side coax can be connected without twisting. This must be done at a later day.
9. Tower was then disassembled so that electrical checks can be performed on the individual electrodes.

The electrical check determined that all LEDs are working properly and can be turned on through the DIB. Bottom electrode (used for charge readout) also showed good connection between Qouter channel and electrode, as well as <1nS between all non-LED channels and chassis. Unfortunately, top electrode (used for HV bias) showed 4.1 MΩ between electrode and chassis. After removing the Qbias screw from the electrode, we determined that this was caused by a ~MΩ between the DIB channels and chassis. We plan to replace the DIB with one of the remaining three DIBS to fix this problem.

Pictures below show the electronics and assembly.

Today the pins on one flexible side coax were reversed (pictures and electrical check to follow), and the top electrode DIB was replaced. An electrical check on this top electrode showed all working as expected EXCEPT a ~mΩ connection between chassis and phonon D channel. It is believed this is due to some excess flux from soldering. Cleaning the DIB with isopropynol reduced the connection to ~2nS. Regardless, this channel is not used, and no other channels are connected.

Today the crystal was mounted into its housing. To do so, 20 mil spares and clamps were put on one side of the crystal housing. A crystal stand was then assembled using a clean room plastic storage tub, some styrofoam that the crystal was packaged with, cut to be slightly smaller than the crystal, and a fabric kim wipe. The housing was set at the base of the stand, around the stand. The crystal was then set on the stand, and the housing was carefully lifted upwards. As it was lifted, the clamps on the bottom side of the housing caught on the crystal, and lifted it up from the stand. The housing and crystal were then gently set down, checking that the crystal was sitting correctly in all the clamps. Then the spacers and clamps on the second side were added, using another fabric kim wipe to guard the crystal from the screws and screw driver (along with a careful hand). Although the designs originally called for two 20 mil spacers on each side, it was determined that one 20 mil spacer was a better fit. It should also be noted that two holes in the housing were not tapped!! and thus one clamp could not be put in.

Figures 1a and 1b: Creating the stand for crystal mounting

Figure 2: Raising the housing to catch the crystal

Figure 3: Crystal is in housing

Figure 4: Clamp screw holes not tapped!

Using a aluminum bar with holes drilled near the edge, and a depth gauge micrometer, we were able to measure the distances from the electrodes and crystal to the edge of the housings. From these measurements we can calculate the gap between each electrode face and its corresponding detector side. We were originally hoping for a gap of 0.5 to 1 mm.

Figure 5: Mechanism to measure distances

Figure 6:NWES orientation for electrodes (DIB to NW)

Due to fears of metal contracting at cold temperatures, additional 5 mil spacers were added to both sides of the detector. New measurements were then made of the detector distances, shown below:

Assembled detector and electrode stack. Used kimwipes to confirm detector and crystal have a ~0.3mm gap.

We discovered that the bias electrode (top UMN orientation) flexible side coax needs to be modified. We'd previously switched the milmax pins to protrude out the back of the pcbs so that the coax could reach the top electrode. Now, we realize that this reversed the tower side pinout. The suggested solution is to restore the tower side pins to their original direction and twist the flexible coax half turn on the way down, restoring the correct pinout.

Figure 1: Flexible Side Coax fit, but we forgot to add shielding

Figure 2: Not all of Dan's shielding designs were used, due to risk of HV sparking on back of soldered pins. Here is what we used.

Figure 3: Here are the Flexible Side Coaxes attached to detector stack^^

Figure 4: New 30 mK can was able to fit over housing with flexible side coaxes attached.

On 2016/03/03 current leakage tests were performed on one of Dan's three flexible side coaxes. Before tests were performed, a quick resistance test was conducted to ensure resistances matched what was inspected. Results shown in table below. It was also noted that flexible side coaxes only have wires connecting Charge pins. Although wires connecting phonon pins will not be necessary, we will likely need wires for the LED pins, since those will likely be connected to the electrode DIB.

These result match was was expected, given the side coax schematic. It was decided that leakage current was to be tested by supplying positive and negative voltages to the Qi Bias and Qo bias pins on the tower side (pins 11 and 14, respectively). Before the negative lead connected to the pin, it would pass through an ammeter to measure any leakage current that might occur. A voltmeter would be hooked up to the leads of the high voltage supply to get a more accurate voltage reading. The test was performed with both orientations of leads to pins. Results shown in table below, but in general no leakage current was seen.

LED 1 and 2 wires were added to two of the flexible side coaxes, using the same wire type used for charge. As following the schematic, these wires connect pins 9 (LED 1) on both sides of the coax, and pins 10 (LED) on both sides of the coax. After soldering, electrical checks were performed to ensure no shorts between pins or to ground.

Tests from 2016/03/24 (Thursday):

Proposed wiring scheme (16 June 2016)

LED choice: IR25-21C/TR8 UV LED choice: E305SL

As the table shows, the traditional LED is an IR LED with a 940 nm (1.32 eV) and provides enough energy to excite to the indirect Si band gap or the Ge direct bandgap. The new UV LED is 310 nm (4.0 eV) and would provide enough energy to excite to the Si direct band gap.

Si Bandgap	Ge Bandgap

LED on PCB (Autodesk model)	PCB Design by Nick Mast

Electrode	Electrode LED	Electrode overhead

Electrode Top Housing

Electrode Bottom Housing

Electrode in Housing
Top Electrode
Bottom Electrode

Electrode Drawing (2016/03/04)