diamond sensor diamond sensor for particle detection maria hempel beam impact meeting geneva,...

Diamond Sensor Diamond Sensor for Particle Detection

Maria HempelBeam Impact MeetingGeneva, 29.8.2014

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


Single Crystal and Polycrystalline Diamond Sensors

> Properties

> Signal Generation

>Diamond Materials

>Differences of Diamond Materials


Diamond Properties

Diamond Advantages:

> Low leakage current (pA)

>No temperature dependence

>Radiation hardness

>Nanosecond time resolution

Diamond Silicon

Band Width (300K) 5.47eV 1.12eV

Electron mobility 2800 cm2.V-1.s-1 1600 cm2.V-1.s-1

e/h pairs for one MIP 36 110

size 5x5mm² (sCVD) or wafer/ 1x1 cm² (pCVD)

wafer


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


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


Differences of Diamond Materials

>Higher initial signal for sCVD than for pCVD

> Fast signal decrease for sCVD

> Slow signal decrease for pCVD

sCVD pCVD

Single MIP counting (CMS) Current monitoring (CMS)

Used for spectroscopy (high energy resolution) Not used for spectroscopy

Higher initial signal 10 times less initial signal

Fast signal decrease with irradiation Slow 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)


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


Optical Inspection

>Using a laser microscope

> Extracted information: Diamond size

Metallization size

thickness

non.-metallized diamondTransparent measurement Thickness calculation

Metallized diamond with two padsInspection of gaps between pads


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


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


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



sCVD- not not selected for installation

sCVD- selected for installation pCVD- selected for installation

pCVD- not selected for installation

CMS11



> Erratic currents for pCVD diamonds

> Effect suppressed under magnetic field (PhD Thesis of Steffen Müller – University of Karlsruhe)

Done by F. Kassel (KIT)


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



>Ramping from 0V to 1kV in different steps

>Different treatment for pCVD & sCVD and for irradiated and non-irradiated diamonds

sCVD pCVD

Non-irradiated 1) 10min illumination with red light

2) Starting CCE ramping

1) 10min red illumination2) 1h pumping with Sr-903a) Starting CCE vs HV (constant HV)3b) Starting CCE vs HV (alternating HV)

irradiated 1) 10min red illumination2) 1h pumping with Sr-903a) Starting CCE vs HV (constant HV)3b) Starting CCE vs HV (alternating HV)

1) 10min red illumination2) 1h pumping with Sr-903a) Starting CCE vs HV (constant HV)3b) Starting CCE vs HV (alternating HV)



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


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 off

Diode on


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

eVEG 4,5eVEG 35.1

4

1


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..


Applications of Diamond Sensors

> Fast Beam Condition Monitor BCM1F

> Front-End of BCM1F Before 2012

>Upgrade BCM1F Front-End


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


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


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)


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


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

diamond sensor diamond sensor for particle detection maria hempel beam impact meeting geneva,...

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