1. 65 nm CMOS analog front-end for pixel detectors at the HL-LHC
Luigi Gaionia,c, F. De Caniob,c, M. Manghisonia,c, Lodovico Rattib,c, Valerio Rea,c, G. Traversia,c
aUniversity of Bergamo
bUniversity of Pavia
cINFN Pavia
TWEPP Topical Workshop on Electronics for Particle Physics September - 02 October, Lisboa

2. Outline The CHIPIX65 project CHIPIX-VFE-1 test structures
Charge sensitive amplifier
Charge sensitivity
Equivalent Noise Charge
Radiation test
Threshold discriminator
Threshold correction circuit
Conclusions
L. Gaioni, TWEPP Topical Workshop on Electronics for Particle Physics

3. The CHIPIX65 project
The INFN CHIPIX65 project aims at the development of an innovative 65 nm CMOS chip for pixel detectors in experiments with extreme particle rates and radiation at future High Energy Physics colliders
This effort is shared at international level with the RD53 Collaboration. CHIPIX65 institutes are part of the funding institutions of RD53 and several key roles of the collaboration are covered by CHIPIX65 members
In the framework of CHIPIX65 a prototype chip called CHIPIX-VFE-1 has been submitted and a comprehensive characterization activity is ongoing
This talk is concerned with the design and the experimental characterization of standalone channels, fundamental building blocks for the development of an innovative pixel front-end chip for the HL-LHC
L. Gaioni, TWEPP Topical Workshop on Electronics for Particle Physics

4. Pixel front-end IK/2 vout Itr=Gm vout CD CF Ith IDAC VREF IK
5 bit ToT counter
Single amplification stage for minimum power dissipation
Krummenacher feedback to comply with the expected large increase in the detector leakage current
High speed, low power current comparator
Relatively slow ToT clock – 80 MHz
5 bit counter – 400 ns maximum time over threshold
30000 electron maximum input charge, ~450 mV preampli output dynamic range
Selectable gain and recovery current
Overall current consumption: ~4 uA
L. Gaioni, TWEPP Topical Workshop on Electronics for Particle Physics

5. Submitted test structures
bias circuits
bias circuits
preampli (MIM feedback cap.) + discri + threshold correction circuit
preampli (MOSFET feedback cap.) + discri + threshold correction circuit
preamplifier with MIM feedback capacitor
preamplifier with MOSFET feedback capacitor
Preamplifier output read out through an on-chip analog buffer
L. Gaioni, TWEPP Topical Workshop on Electronics for Particle Physics

6. Front-end channel configuration
charge sensitivity
0  high gain (CF=10 fF)
1  low gain (CF=20 fF)
recovery current in the Krummenacher network
IK/2
CINJ
0  low recovery current (IK=12.5 nA)
1  high recovery current (IK=25 nA) CD
detector emulating capacitor CF
00  CD=0
10  CD=50 fF
01  CD=100fF
11  CD=150 fF IK
charge injection
0  disabled
1  enabled
L. Gaioni, TWEPP Topical Workshop on Electronics for Particle Physics

7. Charge sensitive amplifier
Folded cascode architecture
Two local feedback networks (M4,M5 and M7,M8) to increase the small signal resistance at the output node
I1=3 µA, I2=200 nA
Simulation data
L. Gaioni, TWEPP Topical Workshop on Electronics for Particle Physics

8. Response to a MIP signal
Response of the preamplifier with feedback MOS capacitor (high and low gain and recovery current)
L. Gaioni, TWEPP Topical Workshop on Electronics for Particle Physics

9. Response to a MIP signal
Response of the preamplifier with feedback MOS capacitor (varying detector capacitance)
Maximum peaking time tp=51.4 ns for a detector capacitance CD=150 fF
Reduced peak amplitude and peaking time with respect to post-layout simulations
L. Gaioni, TWEPP Topical Workshop on Electronics for Particle Physics

10. Response to a MIP signal
Response of the preamplifier with feedback MIM capacitor (varying detector capacitance)
Slightly faster compared to the feedback MOS cap version of the preamplifier
Maximum peaking time tp=43 ns for a detector capacitance CD=150 fF
L. Gaioni, TWEPP Topical Workshop on Electronics for Particle Physics

11. Charge sensitivity
Charge sensitivity, feedback MOS and MIM cap, low recovery current
Standard deviation smaller than 3% of the mean value
INL smaller than 1.5% in all the configurations
Slightly higher charge sensitivity for the preamplifier with feedback MIM capacitor
L. Gaioni, TWEPP Topical Workshop on Electronics for Particle Physics

12. Detector leakage current
Charge sensitivity, evaluated for different values of the detector leakage current
Very small variations due to the detector leakage, both for the feedback MOS and MIM cap version of the preamplifier
L. Gaioni, TWEPP Topical Workshop on Electronics for Particle Physics

13. Equivalent noise charge
ENC for preamplifier with MOS and MIM feedback capacitance
ENC increasing with the preamplifier input capacitance
Higher ENC for the preamplifier configured in low gain mode
Measured ENC in fairly good agreement with simulation data
L. Gaioni, TWEPP Topical Workshop on Electronics for Particle Physics

14. Radiation hardness
Test structures have been irradiated to a TID up to 800 Mrad with 10 MeV protons
No significant changes in charge sensitivity
ENC increase more pronounced for higher values of the total PA input capacitance
24% ENC increase at 800 Mrad, for a total input capacitance of 100 fF
L. Gaioni, TWEPP Topical Workshop on Electronics for Particle Physics

15. Discriminator output and FE response time
Problems with test of the channels with discriminator – likely due to the (quite large) custom designed digital buffer used to read out the discriminator signal. Simulation data shown here
Simulation data
Simulation data
Discriminator current consumption ≈ 1 µA
FE response time < 25 ns for input charge > 900 e- in the tt corner (750 e- threshold)
L. Gaioni, TWEPP Topical Workshop on Electronics for Particle Physics

16. Threshold correction DAC
Global (chip-wide) threshold setting through external (outside the pixel) bias
Local threshold tuning through a 4-bit binary weighted DAC
Power dissipation: ~0.18 uW
L. Gaioni, TWEPP Topical Workshop on Electronics for Particle Physics

17. Threshold correction DAC
Input-output DAC characteristic
INL and DNL for the tested samples
L. Gaioni, TWEPP Topical Workshop on Electronics for Particle Physics

18. Threshold dispersion Simulation data
Threshold dispersion before correction  380 e-
Threshold dispersion after correction  35 e-
L. Gaioni, TWEPP Topical Workshop on Electronics for Particle Physics

19. Conclusions
A prototype chip called CHIPIX-VFE-1 has been submitted in a 65 nm CMOS technology in the framework of the CHIPIX65 project. A comprehensive characterization of the standalone channels has been carried out
Test focused on the charge preamplifier in its different configurations. Problems with the test of the discriminator. A new chip has been submitted in order to fix such problems. Characterization activity of the discriminator starting in the next weeks
Small difference from sample to sample in the main charge preamplifier parameters
With respect to simulation results, experimental ones show a slightly smaller charge sensitivity and a longer peaking time. ENC in fairly good agreement
Radiation hardness test point out that charge sensitivity is not affected by radiation. A moderate increase in the ENC is detected at extremely high TID levels
L. Gaioni, TWEPP Topical Workshop on Electronics for Particle Physics