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BGV x MALTA meeting
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Europe/Zurich
Present: Heinz, Carlos, Bernadette, James, Helene
Agenda: https://indico.cern.ch/event/972988/
MALTA modules for the BGV: Sensor and module geometries for simulations (Helene)
- Sensor
- MALTA chip (23 x 21.3mm) + sensitive area (18.3 x 18.3 mm)
- [Heinz] Die height might be a bit too much
- Loaded geometry of sensor from Carlos' AllPix^2
- But silicon box is 18um thick? [Heinz] this is the sensitive area -> but now the most recent (MALTA2) sensors is 30um. Heinz recommends:
- 10 um circuitry
- 30 um sensitive volume
- 30 to 50 um substrate
- But silicon box is 18um thick? [Heinz] this is the sensitive area -> but now the most recent (MALTA2) sensors is 30um. Heinz recommends:
- MALTA chip (23 x 21.3mm) + sensitive area (18.3 x 18.3 mm)
- Module
- 8+8 -> but inner radius restriction
- 6+6 -> better, but then gaps on the outside
- [Heinz] Internal discussions on MALTA3
- Instead of 4 MATLA-2's -> could have 3 x MALTA-3's (?)
- 7+7 -> better, inner radius "loss" = 1.2mm
- [Heinz] Divide into 4 + 3 for the readout
- [Heinz] Could avoid interfence by stagging in z
- [Heinz] Connect silicon sensors with bump bond "bridge", avoids wire-bonds which would require space (3-4 mm) between the sensors. Wire-bonds require 3-4mm of space; suggest to optimise active area close to the beam pipe
- [Heinz] Consider wedges rather than moons for modules with > 2 rings:
- Minimise the material in the active area (each sub-module => cables);
- Allows to construct in more "bite size" objects;
- Wedges are easier to build rings
- Module positioning
- First station = n_0 rings; Second station = n+0 + 1 rings' Third station = n_0 + 2 rings
- Beam pipe inner diameter = 45. 0mm
- Stations at 59cm; 87cm; 117cm (positions optimised for 7 TeV tracks distribution)
- [Heinz] Comfortable distances; 60cm from first to last layer -> very comfortable distance, in particular, for a common carbon fiber support -> very practical distances (e.g. for cooling, cabling) and not too long for alignment
- [Heinz] Why not consider 4 planes?
- [Helene] Not decided -> to be studied with simulation
- [Heinz] Chances of defining the track are much better with 4 x points
- [Heinz] Rebuilt CMS & ATLAS pixel detectors with 4-layer pixel detector and now going to 5-layers
- [Heinz] Use overlap between planes for alignment -> should have 20%, which is
- [Heinz] Recommends to use a "safe" number of detector planes -> suggests to ask Andy for advice
- [Heinz] Estimates for such a small detector; 50% mechanics & readout & 50% for the detector itself
- [Heinz] 4th layer is usually for the pattern recognition and not the tracking itself
- Misc. consideration
- Do we need CO2 cooling?
- [Heinz] We do need some 2-stage cooling
- [Carlos] ATLAS is moving away from C6F14 for environmental reasons
- [Heinz] Both CO2 & C6F14 are used for the ATLAS pixel detector. CO2 has the advantage of requiring smaller diameter pipes (1.7mm) c.f. C6F14.
- [James] Reason to operate at -20?
- [Heinz] Leakage current doubles every 7 degrees
- [Heinz] Anti-annealing effects -> bias voltage goes up
- [Heinz] Noise improves as
- [Heinz] Need an air tight (environmental) enclosure to flush with nitrogen or dry air to prevent condensation; need cable feedthoughs -> but quite simple
- [Heinz] Not a showstopper to use C6F14
- [Heinz] Need to calculate cooling power
- Do we need CO2 cooling?
MALTA3 (Carlos/Heinz)
News:
- MALTA3 design meeting started last week
- Reviewed limitations of current MALTA / MALTA2 design
- Discussing list of possible applications & calling instiutes for a kick-off meeting
Preliminary discussion:
- New features
- 1ns time resolution -> requires 1 GHz clock -> but chip power prop. clock freq.^2
- Output speed
- Serial powering (daisy chaining)
- Masking -> 1 bit per pixel (enable / disable pixel)
- Pixel shape -> hexagonal pixels to "round out" the corners; [Heinz] Tried out on a small test structure -> avoid some of the effects associated with corners (charge loss and long drift time), but technically difficult to design with current design tools; Will only be done if absolutely necessary
- I2C -> allows communication with a simple device (e.g. Rasperry Pi)
MALTA3 conceptual floorplan:
- Active area = 30mm x 20mm
- Periphery = 30mm x 5mm
- Above limited by TowerJazz 128nm process
- [Heinz] Look of request for 10cm x 10cm modules
- [Heinz] Two years of development for all features (Covid delay included)
- [Heinz] In the mean time possibility start building prototype with MALTA1 (2cmx2cm) and move to MALTA3 once available
- [Heinz] We'll probably need 2 years anyway to understand module building (look at mechanics, cooling and bridge building)
- [Heinz] Kick-off meeting to listen to what people need; will invite BGV team to participate <-> suggests a 10 - 15 mins. introduction presentation
AOB
[Bernadette] Are the calculated hit rates okay?
[Heinz] Need to do a test with X-ray chamber to measure the chip response, but does anticipate a problem
[James] Possible to readout directly with the lpGBT?
[Heinz] Yes it could be possible
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