A. Dorokhov, IPHC, Strasbourg, France 1 Description of pixel designs in Mimosa22 Andrei Dorokhov...

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A. Dorokhov, IPHC, Strasbourg, France

Description of pixel designs in Mimosa22

Andrei Dorokhov Institut Pluridisciplinaire Hubert Curien (IPHC)

Strasbourg, France

03/04/2008

e-mail address: Andrei.Dorokhov@IReS.in2p3.fr

Pixel designs

Standard and Radiation tolerant nwell diode designs Different schematic concepts:

1. Reset diode and standard amplifier (like in Mimosa8)2. Reset diode and amplifier with improved load 3. Continuously biased (self-biased) from feedback and

amplifier with improved load (like in Mimisa15 test structures and Mimosa16)

4. Reset diode from feedback, time variant feedback, amplifier with improved load (similar to Mimosa1819 test structures)

5. Reset diode from feedback, time variant feedback, standard amplifier

CDS with clamping capacitance

Nwell diode designs

Size from 3.4 um x 3.4 um - to 4.5 um x 4.5 um Standard with thick oxide around Nwell Radiation tolerant with thin gate oxide around Nwell

Amplifier schematics (1): standard common source + reset

signal current

Nwell / Pepi

Amplifier schematics (2): improved common source + reset

signal current

Nwell / Pepi

Amplifier schematics (3): improved common source + continuously biased from feedback

(self-biased)

signal current

Nwell / Pepi

Pdiff / Nwell in

Low-pass filter

feedback

Amplifier schematics (4): improved common source + reset from feedback (time-variant

feedback)

signal current

Nwell / Pepi

Time-variant feedback

Amplifier schematics (5): standard common source + reset from feedback (time-variant

feedback)

signal current

Nwell / Pepi

Time-variant feedback

Summary of pixel concepts

(1,2) reset (and amplifier bias) from constant voltage - may be difficult to find working point due to CMOS

process variation - diode leakage current dispersion after irradiation may

significantly degrade performance (3) self-biased from feedback

+ performances should be more stable to process variation

+ diode leakage is compensated by forwardly biased diode

- “pedestal memory effect” from previous hit, even removed after CDS, changing the performance of amplifier

(4,5) reset from feedback + more stable performances for process variation - diode leakage current dispersion after irradiation will

significantly degrade performance

Simulation results

Name ( design concept)

Conversion, [uV/e]

Noise, [uV]

Noise, [e]

Amplifier current, [uA]

S1 (4) 99 728 7 5S2 (4) 89 590 7 5S3 (4) 82 561 7 7S4 (4) 80 570 7 7S5 (4) 83 558 7 7S6 (3) 54 830 15 7S7 (3) 54 828 15 7S8 (3) 51 811 16 7S9 (3) 57 852 15 7S10 (2) 70 544 8 7S11 (4) 72 518 7 9S12 (2) 70 543 8 7S13 (1) 64 440 7 7S14 (5) 68 449 7 4S15 (1) 64 439 7 7S16 (1) 36 318 9 7S17 (1) 34 313 9 7

Simulation with Spectre, parasitic capacitances for diodes, metal lines and transistors are extracted by Frédéric Morel

Measurement results

1. Short results summary of measurements and analysis from Mathieu Goffe:1. S6, S7, S8, S9, S10, S12, S13, S15, S16, S17 are

working fine at standard conditions at 100MHz clock2. For working pixels the charge collection in seed ~30%,

cluster 3x3: 60-80%, in cluster 5x5 : 80-90%, noise from 10e to 13e

3. The other pixels have to be investigated further – one need to vary the frequency, readout pattern, analogue voltages – at least to understand the reason why they don’t show good performances seen in simulations (this is foreseen for the end of April)

2. However, there are at least few working amplifier concepts:1,2,3.

3. Two designs S6 and S10 have different concepts: reset and self-biased from feedback, they are featured with radiation tolerant version of nwell diode -> one can have close look at their performances

Measurement results for S6 and S10

S6, pedestal dispersion + noise

S10, pedestal dispersion + noise

S6, pedestal mean dispersion

S10, pedestal meandispersion

S6, pedestal sigma dispersion

S10, pedestal sigma dispersion

Influence of pixel hit frequency

1. Designs with reset are not sensitive to “memory” effect – charge is always restored to a fixed value

2. Continuously biased diode will store some fraction of charge from previously incident particle, even if the signal completely reconstructed after CDS, there is “internal memory” in the nwell diode -> charge is accumulated and circuit can go to non-linear state

Influence of pixel hit frequency: simulation

1. Single pixel hit frequency 2Hz for 30um x 30um pitch2. Noise – Gaus : SIGMA=15 e3. Signal - Landau distribution: MPV=200e, SIGMA=50e 4. Initial nwell diode voltage 0.7 V5. Amplifier gain -10, offset 1.1 V6. Frame readout (integration time) time 160 us (==1000

pixels in column, 100MHz clock)

Conclusions

1. There two pixel candidates for PHASE1: designs S6 and S10

2. Radiation hardness and hit frequency issues has to be carefully studied for these candidates – one of those may be not suitable for real experiment…

A. Dorokhov, IPHC, Strasbourg, France 1 Description of pixel designs in Mimosa22 Andrei Dorokhov...

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