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65 nm CMOS analog front-endfor 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
TWEPP 2015 - Topical Workshop on Electronics for Particle Physics 28 September - 02 October, Lisboa
aUniversity of Bergamo
bUniversity of Pavia
cINFN Pavia
1
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
2L. Gaioni, TWEPP 2015 - Topical Workshop on Electronics for Particle Physics
The CHIPIX65 project
3
• 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 2015 - Topical Workshop on Electronics for Particle Physics
Pixel front-end
4
• 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
CD
CF
VREF
IK
IK/2
Ith
IDAC
5 bit ToT counter
Itr=Gm vout
vout
L. Gaioni, TWEPP 2015 - Topical Workshop on Electronics for Particle Physics
Submitted test structures
5
preamplifier with MOSFET feedback capacitor
preamplifier with MIM feedback capacitor
preampli (MOSFET feedback cap.) + discri + threshold correction circuit
preampli (MIM feedback cap.) + discri + threshold correction circuit
bias circuits
bias circuits
• Preamplifier output read out through an on-chip analog buffer
L. Gaioni, TWEPP 2015 - Topical Workshop on Electronics for Particle Physics
Front-end channel configuration
6
charge sensitivity
• 0 high gain (CF=10 fF)
• 1 low gain (CF=20 fF)
IK/2
IK
CF
CD
CINJ
recovery current in the Krummenacher network
• 0 low recovery current (IK=12.5 nA)
• 1 high recovery current (IK=25 nA)
detector emulating capacitor
• 00 CD=0
• 10 CD=50 fF
• 01 CD=100fF
• 11 CD=150 fFcharge injection
• 0 disabled
• 1 enabled
L. Gaioni, TWEPP 2015 - Topical Workshop on Electronics for Particle Physics
Charge sensitive amplifier
7
• 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
0
10
20
30
40
50
60
70
80
1 102 104 106 108
Open-loop Gain [dB]
Frequency [Hz]
Preamplifier gain stage
A0 = 76 dB
f-3dB
= 140 kHz
Simulation data
L. Gaioni, TWEPP 2015 - Topical Workshop on Electronics for Particle Physics
Response to a MIP signal
• Response of the preamplifier with feedback MOS capacitor (high and low gain and recovery current)
8
-0.04
-0.02
0
0.02
0.04
0.06
0.08
0.1
0 100 200 300 400 500
Preampli output [V]
Time [ns]
- fb MOS cap
- Qin=10 ke-
high Glow I
K
low Ghigh I
K
high Ghigh I
K
low Glow I
K
L. Gaioni, TWEPP 2015 - Topical Workshop on Electronics for Particle Physics
Response to a MIP signal
• Response of the preamplifier with feedback MOS capacitor (varying detector capacitance)
9
-0.02
0
0.02
0.04
0.06
0.08
0.1
0.12
0 20 40 60 80 100
CD=0
CD=50 fF
CD=100 fF
CD=150 fF
Preampli output [V]
Time [ns]
- high gain- low recovery current
- Qin=10 ke-
21.4 ns
33.3 ns
42.2 ns
51.4 ns
• 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
-0.04
-0.02
0
0.02
0.04
0.06
0.08
0.1
0.12
0 200 400 600 800 1000
CD=0
CD=50 fF
CD=100 fF
CD=150 fF
G
Preampli output [V]
Time [ns]
post layoutsimulations @ C
D=100 fF
- high gain- low recovery current
- Qin=10 ke-
L. Gaioni, TWEPP 2015 - Topical Workshop on Electronics for Particle Physics
Response to a MIP signal
• Response of the preamplifier with feedback MIM capacitor (varying detector capacitance)
10
• 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
-0.02
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0 200 400 600 800
CD=0
CD=50 fF
CD=100 fF
CD=150 fF
Preampli output [V]
Time [ns]
- high gain- low recovery current
- Qin=10 ke-
-0.02
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0 20 40 60 80 100
CD=0
CD=50 fF
CD=100 fF
CD=150 fF
Preampli output [V]
Time [ns]
- high gain- low recovery current
- Qin=10 ke-
17.8 ns
29.7 ns
38.9 ns
43.3 ns
L. Gaioni, TWEPP 2015 - Topical Workshop on Electronics for Particle Physics
Charge sensitivity
• Charge sensitivity, feedback MOS and MIM cap, low recovery current
11
• 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
0
50
100
150
200
250
300
350
0 5 10 15 20 25 30
High gainLow gain
Preamplifier Peak Amplitude [mV]
Injected charge [ke-]
CD = 100 fF
S = 10.4 mV/ke-
S = 5.4 mV/ke-
feedback MOS capacitorlow recovery current
0
50
100
150
200
250
300
350
0 5 10 15 20 25 30
High gainLow gain
Preamplifier Peak Amplitude [mV]
Injected charge [ke-]
CD = 100 fF
S = 11.5 mV/ke-
S = 6.0 mV/ke-
feedback MIM capacitorlow recovery current
L. Gaioni, TWEPP 2015 - Topical Workshop on Electronics for Particle Physics
Detector leakage current
• Charge sensitivity, evaluated for different values of the detector leakage current
12
• Very small variations due to the detector leakage, both for the feedback MOS and MIM cap version of the preamplifier
0
50
100
150
200
250
300
350
0 5 10 15 20 25 30
0 nA10 nA15 nA
Preamplifier Peak Amplitude [mV]
Injected charge [ke-]
CD = 100 fF
feedback MOS capHigh gain, high recovery current
0
50
100
150
200
250
300
350
0 5 10 15 20 25 30
0 nA10 nA15 nA
Preamplifier Peak Amplitude [mV]
Injected charge [ke-]
CD = 100 fF
feedback MIM capHigh gain, high recovery current
L. Gaioni, TWEPP 2015 - Topical Workshop on Electronics for Particle Physics
Equivalent noise charge
• ENC for preamplifier with MOS and MIM feedback capacitance
13
80
100
120
140
160
180
200
-50 0 50 100 150 200
High gainLow gain
ENC [e rms]
PA input capacitance [fF]
feedback MIM capacitancelow recovery current
• 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
60
80
100
120
140
160
180
200
-50 0 50 100 150 200
High gainLow gainpost-layout
ENC [e rms]
PA input capacitance [fF]
feedback MOS capacitancelow recovery current
high gainsimulationdata
L. Gaioni, TWEPP 2015 - Topical Workshop on Electronics for Particle Physics
Radiation hardness
14
• 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
80
100
120
140
160
180
200
220
-50 0 50 100 150 200
fresh500Mrad800Mrad
ENC [e rms]
PA input capacitance [fF]
MOS feedback capacitanceHigh gain, low recovery current
0
50
100
150
200
250
300
350
0 5 10 15 20 25 30
Fresh
500Mrad
Preamplifier Peak Amplitude [mV]
Injected charge [ke-]
CD = 50 fF
feedback MIM capHigh gain, low recovery current
• Test structures have been irradiated to a TID up to 800 Mrad with 10 MeV protons
L. Gaioni, TWEPP 2015 - Topical Workshop on Electronics for Particle Physics
0
0.2
0.4
0.6
0.8
1
1.2
1.4
0 50 100 150 200 250 300
ttffssfssf
Discriminator Output [V]
Time [ns]
Qin = 10 ke-
Four corners simulation
5
10
15
20
25
30
35
40
1 10
Response time [ns]
Input charge [ke-]
t_response < 25 ns @ Qin > 900 e-
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
15
• Discriminator current consumption ≈ 1 µA
• FE response time < 25 ns for input charge > 900 e- in the tt corner (750 e- threshold)
Simulation data
Simulation data
L. Gaioni, TWEPP 2015 - Topical Workshop on Electronics for Particle Physics
Threshold correction DAC
16
• 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 2015 - Topical Workshop on Electronics for Particle Physics
Threshold correction DAC
• Input-output DAC characteristic
• INL and DNL for the tested samples
17L. Gaioni, TWEPP 2015 - Topical Workshop on Electronics for Particle Physics
0.28
0.285
0.29
0.295
0.3
0.305
0.31
0 20 40 60 80 100 120 140 160
beforeafter
Threshold [V]
Pixel cell #
Threshold dispersion
18
Simulation data
• Threshold dispersion before correction 380 e-
• Threshold dispersion after correction 35 e-
L. Gaioni, TWEPP 2015 - Topical Workshop on Electronics for Particle Physics
Conclusions
19
• 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 levelsL. Gaioni, TWEPP 2015 - Topical Workshop on Electronics for Particle Physics