Application of CMOS sensors in radiation detection

S. Ashrafi

Physics FacultyUniversity of Tabriz

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CMOS Complementary Metal Oxide Semiconductor

MOS the MOSFET transistors

Complimentary the two different types of semiconductors (N-type and P-type)

CMOS is used in electronics:

static RAM, digital logic circuits, micro processors, micro controllers, image sensors and particle tracking, and …

CMOS is a technology for making low power integrated circuits.

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Architecture of a CMOS image sensor

photodetector

tran

sisto

rs

access a pixeland read the signal value

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Basic functions of CMOS webcam:

Optical gathering of photons (lens)

Wavelength discrimination of photons (filter)

Detector for photons to electrons conversion (photodiode)

readout the detector

Timing control, and drive electronics

Signal processing electronics

Analog-to–digital conversion

Interface electronics

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Basic configuration of CMOS image sensor.

MSF = source follower transistor

MSEL = select transistor

An n-MOSFET structure is shown:MRS = reset transistor

source is a PD

drain is biased at Vdd

gate is off-state.

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Potential profile

Ohta-2007

The impurity density in the sourceis smaller than that in the drain.

electron density

n MOSFET

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The operation of an APS is as follows:

First, the reset transistor MRS is turned on. This resets VPD to (Vdd −Vth), where Vth is the threshold voltage of transistor MRS.

Then, MRS is turned off and the PD is electrically floated.

When light is incident, the photo-generated carriers accumulate in the PD junction capacitance CPD. The accumulated charge decreases VPD according to the input light intensity.

After an accumulation time of 33 msec , (at video rate), the select transistor MSEL is turned on and the output signal in the pixel is read out in the vertical output line.

When the read-out process is finished, MSEL is turned off and MRS is again turned on to repeat the above process.

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Photodetectors for CMOS image sensors

• behavior of minority carriers is important

• In p-type substrate minorities are electrons

• infrared (IR) penetrate up to 10 μm

• Diffusion of minorities to adjacent photodiodes

• image blurring.

• A PD is usually operated in accumulation mode.

• Photocarriers are swept to the surface due to the potential well in the depletion region

• The potential voltage decreases

• voltage drop ∝ the light powerOhta-2007

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Blooming

The pixels’ potential well has got specified capacity. If quantity of charge is too large, then it diffuses into potential wells of surrounding pixels.

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CMOS: pros & cons listing

1. Low power consumption.

work at low voltage

2. Lower cost

4. Miniaturization

5. Random access of image data

6. High-speed imaging.

1. Lower Sensitivity

2. Higher Noise

3. Small Dynamic range

Fill Factor × Quantum Efficiency

especially under low illumination

Ratio: saturation signal / rms noise floor

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α3He

p

TD

Image sensor preparation for particle detection

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Electron: range – energy in Silicon

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A Bayer filter over the pixel sensor array

2010-Holms

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Camera Sensor Pixels with RGB Color and Infrared Blocking Filters

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computing the size, charge and coordinates of the center of each alpha cluster detected.

measurements in a light tight box 241Am (activity 4.6 kBq) source 5.48 MeV alpha particles

The back-illuminated BT sensor showed nearly 100% efficiency.

Maneuski-2011

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Total Ionizing Dose (TID) –via Dark Current (DC) analysis

1) 60Co irradiation at room temperature2) Sample is unbiased 3) Integration time is 3 seconds 2010-Beaumel

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Thomas Auzinger, 2012

GeigerCam: Measuring Radioactivity with Webcams

use morphological clustering to group pixels into particle impact events and analyze their energies.

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Dead time

The frame rate was 30 Hz, but there were only six different frames per second gathered. It could be caused by large quantity of generated charge that could not be discharged by circuits in the image sensor. The dead time of this detector is 5 cycles, which corresponds to 1/ 6 s, compared to the dead time of Geiger-Müller counters of about 10−4 s

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Radon monitor

2013-Griffin

electrostatic concentrator

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2013-Griffin

β

α

Radon measurements:

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Linearity & Sensitivity

Kang 2016

2) For X-rays, the bluecomponent has higher sensitivity

1) The excellent linearity

Sensor has a thickness of less than 10 μm

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X-ray energy dependence

Kang 2016

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Gamma-ray dose rate dependence 137CS: 662 keV

Kang 2016

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Other Gamma-rays

Kang 2016

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CellRAD is a system of software that runs on off-the-shelf unmodified Android cellphones. It uses the camera of the phone to detect gamma radiation.

CellRAD

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Dark current distribution – low dose

CMOS CHARACTERISTICS

Dark current spectroscopy: Second peak is related to deep-level traps

Shift of distributionDue to TID

2014-Virmontois

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Dark current distribution – high dose

Shift of distributionDue to TID

Spikes are related to Displacement damages

2014-virmontois

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CMOS image sensors as X-ray imagers

High-resolution X-ray micro-imaging X-ray beam monitor

2015-Castoldi

1 mm

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CMOS image sensors as particle beam monitors

1 up to 6 MeV proton beam

Image of a single 1 MeV proton detection.

2015-Castoldi

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Fixed Pattern Noise (FPN) Suppression

2015-Perez

-5σ

The CMOS imager: Commercial APTINA MT9V011

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55Fe: 5.90 keV or 6.5 keV X-ray

137Cs(γ –ray): 662 keV

137Cs( β–ray): 514, 1176 keV

Response of CMOS toγ, β – rays and α particles

2015-Perez 32

2018-Prez

Response of CMOS to neutrons

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phosphorus-32 β particleEmax= 1711 keV

Am-241 α particleE= 5485, 5443, 5388 keV

2018-Nelson

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PhotodiodeSensor(PD)

MonolithicActive Pixel Sensor (MAPS)

ComplementarySensor Active Pixel sensor(CAPS)

ImprovedFill factor

diffusion

ImprovedFill factor

drift

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2008-Rao

A 4-T APS structure

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Disadvantages:

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Complementary active pixels sensors (CAPS)

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Apply bias voltage to bulk rely on drift instead of diffusion

Take care of inter-pixel isolation

Avoid charge collection on parasitic wells by shielding them inside a deep n-well

The main new features are that the reset transistor is replaced by a PMOS.

Complementary active pixels sensors (CAPS)

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Pixelated Silicon as a sensor:

Keller

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Pixelated SiliconKeller

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Pattern Recognition:

Keller

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a neutron-induced reaction with three ejected evaporation particles

2014-Saoud

a high-energy proton---- or----------

different topology shapes detected with a CCD

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Conclusions:

CMOS sensors are applicable to:

Radiation dosimetry

Particle tracking

X-ray imaging

Particle identification

Beam monitoring

CMOS sensors are available at low cost (COTS)

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Ohta, J. (2007). Smart CMOS image sensors and applications. CRC press.

References:

Holms, A., & Quach, A. (2010). Complementary Metal-Oxide Semiconductor Sensors.

Maneuski, D., Blue, A., Hynds, D., Mac Raighne, A., & O'Shea, V. (2011). Evaluation of silicon active pixel sensors for alpha particle detection. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 659(1), 328-332.

Beaumel, M., Herve, D., & Van Aken, D. (2010). Cobalt-60, proton and electron irradiation of a radiation-hardened active pixel sensor. IEEE Transactions on Nuclear Science, 57(4), 2056-2065.

Auzinger, T., Habel, R., Musilek, A., Hainz, D., & Wimmer, M. (2012, August). GeigerCam: measuring radioactivity with webcams. In SIGGRAPH Posters (p. 40).

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References:

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“Classical MAPS” → HV/HR-CMOS■ Apply bias voltage to bulk → rely on drift instead of diffusion■ Avoid charge collection on parasitic wells by shielding them inside adeep n-well■ Take care of inter-pixel isolation after irradiation by suitable techniques■ Often a rather classical charge-sensitive amplifier with leakage currentcompensation is used at the expense of larger pixels■ New applications opening up?

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