Institut fr Kernphysik Frankfurt for the CBM-MVD-collaboration - PowerPoint PPT Presentation

AD vanced MO nolithic S ensors for An X-ray fluorescence spectrometer using CMOS-sensors Dennis Doering, Michael Deveaux Institut für Kernphysik Frankfurt for the CBM-MVD-collaboration Sensor development: IPHC Strasbourg 1) Real-time water analysis using XRF 2) CMOS-Sensors 3) Reconstruction of the energy information 4) Improving the quantum efficiency 1 Supported by BMBF (06FY9099I and 06FY7113I), HIC for FAIR, GSI and EU-FP7

Application: X-ray spectrometer Monitoring water quality and trigger on traces of pollution Sample Identifing elements via their characteristic X-ray-fluorescence lines (XRF) Required sensor features: - Good energy resolution - Low noise - High-rate capability - Low production costs ⇒ Adapted CMOS-sensors M. Deveaux, D. Doering: An XRF spectrometer using CMOS-sensors DPG Darmstadt March 2016 2 /25 /17

Operation principle of CMOS-sensors SiO 2 SiO 2 SiO 2 N+ P-Well N+ P+ Diode e- P- Depleted zone Epitaxial Layer e- P+ Substrate Particle M. Deveaux, D. Doering: An XRF spectrometer using CMOS-sensors DPG Darmstadt March 2016 3 /25 /17

Charge smearing between pixels One pixel: Fluorescence spectrum of the setup 1000 One "seed" pixel P-Well Diode +20°C 800 e- Depleted P- Epitaxial Layer e- Counts [1/36e] zone P+ 600 Photon 400 Pixel charge smearing 200 Ag K α (cal) Cd-109-source Ag K β (support is built up Ag K α ,K β of brass) 0 2 4 6 8 10 12 14 16 18 20 22 24 26 Collected electrons [ke] Chip (PCB contains Ba) Drawback: Charge smearing M. Deveaux, D. Doering: An XRF spectrometer using CMOS-sensors DPG Darmstadt March 2016 4 /25 /17

Cluster of 25 pixels Cluster of 25 pixels Fluorescence spectrum of the setup 1000 One "seed" pixel Cluster P-Well Diode +20°C 800 Ag K α (cal) e- Depleted P- Epitaxial Layer e- Counts [1/36e] zone Ba L α P+ 600 Photon 400 Cu K α 200 Ag K β Cd-109-source (support is built up Ag K α ,K β of brass) 0 2 4 6 8 10 12 14 16 18 20 22 24 26 Collected electrons [ke] Chip (PCB contains Ba) Disadvantage: Noise contribution of 25 pixels M. Deveaux, D. Doering: An XRF spectrometer using CMOS-sensors DPG Darmstadt March 2016 5 /25 /17

Trigger on conversions in the depleted zone Fluorescence spectrum of the setup Depleted zone P-Well Diode 250 +20°C e- e- Depleted P- Epitaxial Layer Counts [1/36e] 200 zone P+ 150 Ba L α Photon 100 Ag K α (cal) Cu K α 50 Zn K α V K α Cd-109-source Ag K β (support is built up Ag K α ,K β 0 of brass) 0 2 4 6 8 10 12 14 16 18 20 22 24 26 Collected electrons [ke] Chip (PCB contains Ba) Triggercondition: Neighboring pixel carry no charge M. Deveaux, D. Doering: An XRF spectrometer using CMOS-sensors DPG Darmstadt March 2016 6 /25 /17

Trigger on conversions in the depleted zone Fluorescence spectrum of the setup 1000 Depleted zone 950 Cluster 900 P-Well Diode +20°C 850 e- e- 800 Depleted 750 P- Epitaxial Layer Counts [1/36e] 700 zone 650 P+ 600 550 Ba L α 500 Photon 450 400 350 300 Ag K α (cal) 250 Cu K α 200 150 Zn K α V K α Cd-109-source 100 Ag K β 50 (support is built up Ag K α ,K β 0 of brass) 0 2 4 6 8 10 12 14 16 18 20 22 24 26 Collected electrons [ke] Chip (PCB contains Ba) Drawback: Reduced quantum efficiency M. Deveaux, D. Doering: An XRF spectrometer using CMOS-sensors DPG Darmstadt March 2016 7 /25 /17

Linearity of amplification chain Ag K β +20°C 25 Energy of the identified peak [keV] Ag K α 20 15 10 Cu K α Zn K α Mn K β Ba L α Mn K α 5 V K α Energy[keV]=(0.0364±0.0004) · Q coll [ADC]+(-0.004±0.05) 0 0 100 200 300 400 500 600 700 Charge collected [ADC] Linear energy scale at least between a few keV up to 25keV M. Deveaux, D. Doering: An XRF spectrometer using CMOS-sensors DPG Darmstadt March 2016 8 /25 /17

Strategies to increase the quantum efficiency High-resistivity: Decrease of doping concentration in epitaxial layer. Depletion voltage: Increase the depleted volume Low-resistivity ~ 30 Ω cm High-resistivity ~1k Ω cm SiO 2 Sensing diode P-Well N+ P+ P- Epitaxial Layer Substrate P+ depleted volume Larger depleted volumes: ⇒ Accelerated charge collection, less diffusion ⇒ Less charge smearing between pixels Aim: Full depletion of the epitaxial layer M. Deveaux, D. Doering: An XRF spectrometer using CMOS-sensors DPG Darmstadt March 2016 9 /25 /17

TOWER-Jazz-Process High-resistivity: Decrease of doping concentration in epitaxial layer. Depletion voltage: Increase the depleted volume Low-resistivity ~ 30 Ω cm High-resistivity ~1k Ω cm TOWER-Jazz-0.18µm process - High-Resistivity 1-8k Ω cm SiO 2 - Depletion voltage up to 20V Sensing diode P-Well N+ P+ P- Epitaxial Layer Substrate P+ depleted volume Modified preamplifier Larger depleted volumes: - Recharge diode ⇒ Accelerated charge collection, less diffusion - AC-coupled ⇒ Less charge smearing between pixels Aim: Full depletion of the epitaxial layer M. Deveaux, D. Doering: An XRF spectrometer using CMOS-sensors DPG Darmstadt March 2016 10 /25 /17

TOWER-Jazz 0.18µm CMOS process for imager The Sensor: PEGASUS (2015) 18µm thick, 25µm pixel pitch, >1k Ω cm epitaxial layer, 12 V bias voltage Pegasus, T= +20°C Cd-109-source Ag L α One "seed" pixel 300 Counts [1/40 e] Cd-109-source 225 Cu K α Ag K α ,K β Ag K α Calibration peak Cu-foil 150 Cu K β 75 Ag K β 0 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 Less charge smearing Collected energy [keV] ⇒ Larger depletion zone M. Deveaux, D. Doering: An XRF spectrometer using CMOS-sensors DPG Darmstadt March 2016 11 /25 /17

TOWER-Jazz 0.18µm CMOS process for imager The Sensor: PEGASUS (2015) 18µm thick, 25µm pixel pitch, >1k Ω cm epitaxial ayer, 12 V bias voltage Pegasus, T= +20°C Cd-109-source Ag L α One "seed" pixel 300 Depleted zone Counts [1/40 e] Cd-109-source 225 Cu K α Ag K α ,K β Ag K α Calibration peak Cu-foil 150 Cu K β 75 Ag K β 0 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 Less charge smearing Collected energy [keV] ⇒ Larger depletion zone Trigger on neighboring pixels still helps M. Deveaux, D. Doering: An XRF spectrometer using CMOS-sensors DPG Darmstadt March 2016 12 /25 /17

Influence of the leakage current T= +20°C Cu-K α = 8135 eV Literature: 1000 600 Cu-K α 1 =8047 eV T= -20°C Cu-K α = 8035 eV T= +20°C 550 900 Cu-K α 2 =8027 eV T= -20°C 500 800 Counts [1/80 e] Counts [1/80 e] 450 700 400 600 σ +20°C =637eV 350 σ -20°C =215eV 500 300 250 400 200 300 150 200 100 100 50 0 0 6,0 6,5 7,0 7,5 8,0 8,5 9,0 9,5 10,0 20,0 20,5 21,0 21,5 22,0 22,5 23,0 23,5 24,0 Collected energy [keV] Collected energy [keV] Due to the non-linear response of the recharge diode at +20°C : - Limited energy resolution - Non-linear amplification ⇒ Optimizing of the pixel layout required (Pegasus-3) ⇒ Cooling to -20°C so far helps M. Deveaux, D. Doering: An XRF spectrometer using CMOS-sensors DPG Darmstadt March 2016 13 /25 /17

Cu-inlay Pegasus, T= -20°C Cd-109-source (norm. to detected Ag K α -Photons) 1350 Reference 1200 Cu-inlay 1050 Counts [1/80 e] Cu K α =8040 eV Cd-109-source 900 σ =122eV Ag K α ,K β 750 Ag K α Cu-foil 600 Ag K α ,K β +Cu K α 450 Ag L α 300 Ag K β Cu K β 150 0 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 Collected energy [keV] Expected excess in Cu-K α -line observed Energy resolution is σ =122eV M. Deveaux, D. Doering: An XRF spectrometer using CMOS-sensors DPG Darmstadt March 2016 14 /25 /17

Conclusion Application: Real-time water analysis via X-ray fluorescence analysis ⇒ CMOS-Sensors proposed Studied two CMOS-sensors: MIMOSA-19 and Pegasus Possible above 2 keV with an energy resolution of 120…190eV At room temperature or slightly cooled conditions ⇒ Sensors seem suited for the task Outlook: Obtain higher quantum efficiency due to full depleted epitaxial layer Detailed study of high-voltage CMOS-sensors required DFG proposal submitted M. Deveaux, D. Doering: An XRF spectrometer using CMOS-sensors DPG Darmstadt March 2016 15 /25 /17