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 2015 - Topical Workshop on Electronics for Particle Physics 28 September - 02 October, Lisboa

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 2015 - Topical Workshop on Electronics for Particle Physics

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 2015 - Topical Workshop on Electronics for Particle Physics

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 2015 - Topical Workshop on Electronics for Particle Physics

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 2015 - Topical Workshop on Electronics for Particle Physics

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 2015 - Topical Workshop on Electronics for Particle Physics

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 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) 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) 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 2015 - Topical Workshop on Electronics for Particle Physics

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 2015 - Topical Workshop on Electronics for Particle Physics

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 2015 - Topical Workshop on Electronics for Particle Physics

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 2015 - Topical Workshop on Electronics for Particle Physics

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 2015 - Topical Workshop on Electronics for Particle Physics

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 2015 - Topical Workshop on Electronics for Particle Physics

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 2015 - Topical Workshop on Electronics for Particle Physics

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 2015 - Topical Workshop on Electronics for Particle Physics

Threshold correction DAC Input-output DAC characteristic INL and DNL for the tested samples L. Gaioni, TWEPP 2015 - Topical Workshop on Electronics for Particle Physics

Threshold dispersion 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 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 2015 - Topical Workshop on Electronics for Particle Physics