1. Diamond Sensor Diamond Sensor for Particle Detection Maria Hempel Beam Impact Meeting Geneva, 29.8.2014

2. Maria Hempel | Beam Impact Meeting | 29.8.2014 | Seite 2 Table of Content > Single Crystal and Polycrystalline Diamond Sensors > Characterization Setups > Polarisation > Application of Diamond Sensors

3. Maria Hempel | Beam Impact Meeting | 29.8.2014 | Seite 3 Single Crystal and Polycrystalline Diamond Sensors > Properties > Signal Generation > Diamond Materials > Differences of Diamond Materials

4. Maria Hempel | Beam Impact Meeting | 29.8.2014 | Seite 4 Diamond Properties Diamond Advantages: > Low leakage current (pA) > No temperature dependence > Radiation hardness > Nanosecond time resolution DiamondSilicon Band Width (300K)5.47eV1.12eV Electron mobility2800 cm 2.V -1.s -1 1600 cm 2.V -1.s -1 e/h pairs for one MIP36110 size5x5mm² (sCVD) or wafer/ 1x1 cm² (pCVD) wafer

5. Maria Hempel | Beam Impact Meeting | 29.8.2014 | Seite 5 Signal Generatiion > Diamond are operated as solid state ionization chamber > Ionization of atoms by MIP particles  36 e/h pairs/μm  Usual thickness of diamond: ~300μm or ~500μm > Metallization of diamond surface  Tungsten/Titanium  CMS diamonds  Chromium/Gold  BCM1F4LHC diamonds > Separation of e/h pairs due to bias voltage  Number of separated e/h depends on bias voltage  Above certain bias voltage maximum number of separated e/h is reached  Different for each diamond

6. Maria Hempel | Beam Impact Meeting | 29.8.2014 | Seite 6 Diamond Materials > Diamond is grown by chemical vapor deposition  CMS used diamonds are from E6 (sCVD and pCVD) and II-VI (pCVD)  Usage of seed crystal in a cloud of plasmatic methane gas  heated by microwave energy  carbon atoms attach on seed crystal with diamond configuration > Single crystal diamond:  grown on High Temperature High Pressure Diamond  5x5mm² size > Polycrystalline diamond  grown on diamond powder attached on silicon  Wafer size Cross section through pCVD diamond grainboundaries occur during growing process Thesis S. Müller

7. Maria Hempel | Beam Impact Meeting | 29.8.2014 | Seite 7 Differences of Diamond Materials > Higher initial signal for sCVD than for pCVD > Fast signal decrease for sCVD > Slow signal decrease for pCVD sCVDpCVD Single MIP counting (CMS)Current monitoring (CMS) Used for spectroscopy (high energy resolution)Not used for spectroscopy Higher initial signal10 times less initial signal Fast signal decrease with irradiationSlow signal decrease with irradiation Single crystal structure allows better understanding of physics (charge carrier transport, radiation damage) Polycrystalline structure makes simulation more complicated “Radiation damage in diamond detectors for beam monitoring at CMS” (M. Guthoff)

8. Maria Hempel | Beam Impact Meeting | 29.8.2014 | Seite 8 Diamond Characetrization > Every diamond is different in electrical properties > Choosing the best diamond sensors for later operation > Characterization measurements:  Optical inspection  Leakage current as a function of bias voltage  Signal stability as a function of time  Charge collection efficiency (CCE) as a function of bias voltage  CCE as function of time for irradiated diamonds

9. Maria Hempel | Beam Impact Meeting | 29.8.2014 | Seite 9 Optical Inspection > Using a laser microscope > Extracted information:  Diamond size  Metallization size  thickness non.-metallized diamond Transparent measurement Thickness calculation Metallized diamond with two pads Inspection of gaps between pads

10. Maria Hempel | Beam Impact Meeting | 29.8.2014 | Seite 10 Leakage Current as a Function of Bias Voltage > Diamond inside frame > Bonding of diamond > Installing frame in a shielding box > Shielding box is filled with nitrogen > Measuring leakage current as function of HV  -1kV to +1KV > Leakage currents has to be in the order of pA

11. Maria Hempel | Beam Impact Meeting | 29.8.2014 | Seite 11 Leakage Current as a Function of Bias Voltage sCVD- selected for installation sCVD- not selected for installation pCVD- selected for installation pCVD- not selected for installation

12. Maria Hempel | Beam Impact Meeting | 29.8.2014 | Seite 12 Signal Stability as a Function of Time > Same setup as leakage current as function of HV > Adding a Sr-90 source to generate signal current > Measurement settings:  -500V for 5h  0V for 1h  +500V for 5h  0V for 1h > Expected signal current: ~ 10E-9 Sr-90

13. Maria Hempel | Beam Impact Meeting | 29.8.2014 | Seite 13 Signal Stability as a Function of Time sCVD- not not selected for installation sCVD- selected for installation pCVD- selected for installation pCVD- not selected for installation CMS11

14. Maria Hempel | Beam Impact Meeting | 29.8.2014 | Seite 14 Signal Stability as a Function of Time > Erratic currents for pCVD diamonds > Effect suppressed under magnetic field (PhD Thesis of Steffen Müller – University of Karlsruhe) Done by F. Kassel (KIT)

15. Maria Hempel | Beam Impact Meeting | 29.8.2014 | Seite 15 CCE as a Function of Bias Voltage > Measures the collected charge at different voltages > Signal generation by electrons from Sr-90 (triggered by scintillators) > Applying bias voltage by HV table > Readout of signal with needle > Using connecting bond for two pad metallization > Possibility to switch on red diode light

16. Maria Hempel | Beam Impact Meeting | 29.8.2014 | Seite 16 CCE as a Function of Bias Voltage > Ramping from 0V to 1kV in different steps > Different treatment for pCVD & sCVD and for irradiated and non- irradiated diamonds sCVDpCVD Non-irradiated1)10min illumination with red light 2)Starting CCE ramping 1) 10min red illumination 2) 1h pumping with Sr-90 3a) Starting CCE vs HV (constant HV) 3b) Starting CCE vs HV (alternating HV) irradiated1) 10min red illumination 2) 1h pumping with Sr-90 3a) Starting CCE vs HV (constant HV) 3b) Starting CCE vs HV (alternating HV) 1) 10min red illumination 2) 1h pumping with Sr-90 3a) Starting CCE vs HV (constant HV) 3b) Starting CCE vs HV (alternating HV)

17. Maria Hempel | Beam Impact Meeting | 29.8.2014 | Seite 17 CCE as a Function of Bias Voltage sCVD before and after irradiation of 24GeV proton equivalent (3.5 ·10E12 proton equivalent per fb−1) pCVD before and after very high irradiation (taken from “Radiation Damage in the Diamond Based Beam Condition” Monitor of the CMS Experiment at the LHC at CERN” M. Guthoff et al.) Constant HV alternating HV Constant HV sCVD with constant HV and alternating HV

18. Maria Hempel | Beam Impact Meeting | 29.8.2014 | Seite 18 CCE as function of time for irradiated diamonds > Same setup as for CCE vs HV > Constant HV (500V) > Monitoring CCE as a function of time  Decrease of CCE can be observed > Decrease can be suppressed by red diode light 500V Diode off Diode on Diode off Diode on

19. Maria Hempel | Beam Impact Meeting | 29.8.2014 | Seite 19 Polarization > Radiation damages the diamond crystal > Traps are created  Band gap at  Hypothesis: deep traps are at > Process of polarization:  Bias voltage is switched on  Sr-90 source creates e/h pairs  Free charge carrier density is larger at diamond edges  Traps are filled by free charge carriers  asymmetric filling due to charge carrier density  Creation of space charge in the bulk  Compensation of external electrical field by internal field  Polarization > Red light energy at 1.9eV  Releasing the trapped charge carriers

20. Maria Hempel | Beam Impact Meeting | 29.8.2014 | Seite 20 Polarization – Possible Solutions > Pumping of diamond with Sr-90 source for ~1h  All traps are filled  Constant CCE over time  CCE reaches a minimum for the whole measurement > Permanent illumination with red light  Red light energy is 1.9eV  Releases trapped charge carriers  CCE reaches a maximum for the whole measurement  Red diode needs to be radiation hard! > Using alternating polarity of HV (2-0.5Hz)  Polarization cannot develop  CCE is enhanced For our characterization we use mainly pumping. For study purpose we also make diode measurements and HV with alternating polarity..

21. Maria Hempel | Beam Impact Meeting | 29.8.2014 | Seite 21 Applications of Diamond Sensors > Fast Beam Condition Monitor BCM1F > Front-End of BCM1F Before 2012 > Upgrade BCM1F Front-End

22. Maria Hempel | Beam Impact Meeting | 29.8.2014 | Seite 22 The Fast Beam Condition Monitor > Radiation hard beam condition monitor with ns time resolution > Monitors luminosity and beam background  Counting MIPs > Before 2012 it contained 4 sCVD diamonds on each side of the CMS interaction point  1.8m away from the CMS IP

23. Maria Hempel | Beam Impact Meeting | 29.8.2014 | Seite 23 Front-End of BCM1F Before 2012 > One pad diamonds > Signal generation by MIP > Charge conversion to output voltage  20mV/fC > Signal shaping  Peaking time of 25ns > Optical conversion with laser diode  Optical driver 5cm from beam center > Optical signal is sent to counting room One pad diamond (5x5mm²) Amplifier and shaper Optical converter

24. Maria Hempel | Beam Impact Meeting | 29.8.2014 | Seite 24 BCM1F Front-End during Operation > Radiation damage of laser diode (laser driver)  Decrease of dynamic range > Monster signals  Overshoot of signals  Saturation of laser driver  Long recovery time > High signal rates for 25ns  Two MIPs with 12.5ns cannot be resolved Long rise time (~25ns) Time-over- threshold (~100ns) Overshoot (few μs)

25. Maria Hempel | Beam Impact Meeting | 29.8.2014 | Seite 25 Upgrade of BCM1F Front-End > Using 12 sCVD diamonds on each side of CMS IP  Higher acceptance for background > Two pad metallization  Reducing the signal occupancy (more dynamic range) > Dedicated front-end ASIC (amplifier) from Krakow University  Less than 10ns FWHM  Conversion of 50mV/fC > Different position of laser driver  16cm away form beam center Peaking time of 10ns with 2ns ADC sampling time Testbeam Signal with new Amplifier

26. Maria Hempel | Beam Impact Meeting | 29.8.2014 | Seite 26 Summary > Diamonds can be fully characterized in Zeuthen with different techniques  Leakage current, signal stability, CCE > Signal sizes depend on diamond material and absorbed dose  Possible explanation is polarization > Diamond based Condition Monitor was successfully running > After LS1 an upgraded BCM1F system is prepared in order to face the new challenges