Timeline of development

  1. Medipix1
  2. Medipix2
  3. Mpix2MXR20
  4. Timepix
    1. src: Xavier
  5. Medipix 3
  6. Timepix 3
  7. Smallpix
  8. VeloPix

Medipix

  • Hybrid detector, meaning
    • A detecting layer and a logic layer.
    • Layers bump bonded.
    • 'Naked' operation of the logic layer possible.
  • Therefore very adaptable to various applications.

Effects

  • Crosstalk
    • The effect that charge in the semicon diffuses to other pixels and generate a hit there. Because this takes some time, time Timepix mode this is easy to get rid of: late signals are late tracks or crosstalk.
  • Charge sharing
    • Is the name of Diffusion in solid state materials.
    • This means that the semicon substrate doesn't confine single charges to single pixels, but that due to the layer thickness and diffusion there is room for the charges to spread over an area spanning multiple pixels.
    • Panos writes this limits energy resolution. How?
    • Ask Enrico why you don't want charge sharing. I think it could be beneficial.
  • Equalization
    • Each pixel has an offset and should be equalized, so that pixels have a similar readout. So what exact property has an offset?
    • How does it exactly work? Panos will get back to me. See Panos 2.1.1 and Electronics.
    • This equalization is both Digital and Analog.
    • Image on p68 Xavier
    • Three correction masks are generated for each equalization procedure. Not important for me, still interesting
      • raw, only pixels in bad columns are masked this means corrected in any way?
      • fine1, pixels with threshold > 3.2 sigma are masked what does this mean?
      • fine2, a number close to MaxMasked is masked why is this usefull?
  • Energy loss
    • See 3.1 Veerle.
  • Angled Incidence
    • See 3.2 Veerle.

Sensors

One can use different sensors on top of the chip, solid state and gas (where the ionisation electrons are amplified by a Micromegas-like grid). Solid state is radiation hard and durable, but has a lot of stopping power. Therefore a grid with an applied electric field is used to create a small drift chamber with a chip as anode. Gas has almost no stopping power and is therefore perfectly suited for monitoring hadron beams. This grid-like setup can be found in GridPix.

Versions

Timepix

The Medipix2 and Mpix2MXR20 chips have shown great potential in different applications requiring single photon counting approach. Successful tests using the chips for the readout of a TPC 15 prototype for the ILC 16 showed very promising results when coupled to Gas Electron Multipliers (GEM) or Micromegas gain grids (papers VIII and IX). Although these experiments demonstrated that single primary electrons could be detected, the chip did not provide information on the arrival time of the electron in the sensitive gas volume nor on the quantity of charge deposited.
The Timepix chip is an evolution from the Mpix2MXR20 chip which allows for measurement of arrival time, “time-over-threshold” (TOT) and/or event counting independently in each pixel. An external reference clock (Ref_Clk) is used to generate the clock in each pixel that increments the counter depending in the selected operation mode with a maximum frequency of 100 MHz. The chip has the same dimensions readout architecture and floor plan as the Mpix2MXR20 chip allowing almost full backward compatibility with all the existing Medipix2 readout systems (see section 3.1).

Timepix can measure either:

  • ToT, time over threshold.
    • The time that the signal is over a certain lower threshold THL.
    • Proporional to the charge deposited on the pixel.
  • ToA, time of arrival.
    • Also ToF (time of flight).
    • The time from when the signal went over threshold until the the end of the shutter time. This means that higher values, i.e. longer times, correspond to earlier events, i.e. that happened closer to the chip.
    • Resolution: 10 ns.
  • Simply count hits.
In the future Timepix3 it is foreseen to use two counters to measure ToT and ToA simultaneously.

Medipix with solid state detector attached

The detecting layer could be a regular of the semiconductortype. For example: a grating of p-type material to attract electrons to the 'pixels' (bump bonds) and a huge slab of n-type material on top (silicon). Charged particles generate electron-hole pairs in the silicon and an electric potential causes drift of these towards the bumpbonds, where the logic chip captures and processes the data.

More: Semiconductors.

Medipix3

  • Charge sharing is mitigated with a new readout mode called Charge Summing Mode.
    • On 2x2 pixel blocks, charge is summed and assigned to the pixel with the largest charge deposition.
    • No src. Question: which 2x2 blocks? Regular old grid?
    • This is done event by event.
  • Radiation hard
    • Because its built on 130 nm, there is less material to 'pollute' with charges.
-- RolfS - 2012-02-08
Topic revision: r5 - 2012-02-22 - NielsVanBakel
 
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