1. Characterisation of Active Pixel Sensors
Dima Maneuski
1st year PhD Student
University of Glasgow

2. Outline What is APS? What is CCD? Vanilla APS HEPAPS4
What do we actually need to characterise?
Photon transfer technique
Experimental setup
Status on Prague activity

3. We live here in Kevin Building

4. Basic CCD camera Advantages: Low noise; High full-well capacity;
100% fill factor;
High uniformity;
Mature technology;
Disadvantages:
Slow readout;
Pixel blooming;
Specialised fabrication;
Low functionality;

5. Basic CMOS camera Advantages: High Speed readout; Random access;
On-chip intelligence;
Low power consumption;
Disadvantages:
High read-out noise;
Reduced dynamic range;
Reduced uniformity;
Reduced fill-factor;
High cost;

6. Vanilla APS 512 x 512 pixels – 25 mm square Fill Factor ~ 85 %
Optional soft/hard/flushed
Analogue and digital output
up to 100 fps at 12 bit digital output
Flexible ROIs (up to 6 x 20kHz in analogue output)
100k –e full well capacity

7. Flushed Reset
Soft reset results in a lowered reset noise (kTC/2)1/2 instead of (kTC)1/2
However, frames taken utilising soft reset are affected by image lag, where the current image is affected by the previous frame.
Using hard reset, image lag is overcome, but results in full (kTC)1/2 noise and reduced full well capacity.
By using a hard reset followed by a soft reset, it is possible to get the best of both reset methods. This is known as flushed reset.

8. Region of Interest 12 bit digital output for full frame mode.
Region of Interest (ROI) readout for up to 6 ROI (6 x 6 pixels/ROI).
20kHz analogue readout at 10 bits resolution for ROI.
520x520 – 4fps
200x200 – 28fps
50x50 – 432fps

9. HEPAPS4 1024 x 384 pixels – 15 mm square 100 % efficiency for MIPs
20um epi
Radiation hard ( > Mrad) (?)

10. Spectral Response
Refers to the detected signal response as a function of the wavelength of light. Often expressed in terms of the Quantum Efficiency, a measure of the detector's ability to produce an electronic charge as a percentage of the total number of incident photons that are detected.

11. Dynamic Range
A measure of the maximum and minimum intensities that can be simultaneously detected in the same field of view. It is often calculated as the maximum signal that can be accumulated, divided by the minimum signal which in turn equates to the noise associated with reading the minimum signal. It is commonly expressed in decibel scale.
Camera Gain
The camera gain is the conversion factor that relates the ADU value to the number of electrons collected by a pixel.
Signal to Noise Ratio
The comparison measurement of the incoming light signal versus the various inherent or generated noise levels, and is a measure of the variation of a signal that indicates the confidence with which the magnitude of the signal can be estimated.

12. Linearity
non-linearity
is based on the error between the best-fit straight-line to the original data of the camera input vs. the camera mean response at each illumination level, in ADU’s

13. Noise, noise, noise… • Read Noise: inherent output amplifier noise
• Dark Noise: thermally induced noise arising from the camera in the absence of light
• Shot Noise (Light Signal): noise arising out of the stochastic nature of the photon flux itself
Sensor
Photon noise, dark current, fixed pattern noise, and shot noise
Electronics
reset noise, quantization noise

14. Photon Transfer Curve Measuring noise with noise
The camera is a system block with light as an input, and digital data as an output
The only noise introduced at the input is shot noise.
Any difference between the noise at the input and the noise at the output is sensor and/or electronics noise.
Mean = S (signal)
Standard deviation = S1/2 (Noise)

15. Photon Transfer Curve Direct data Read noise Gain Full well
Indirect data
Dynamic range
SNR
Linearity (if power of LED is known)

16. HEPAPS4 PTC

17. Vanilla
Performance Parameter
Value
Units
Camera Gain
10.9
electrons/DN
Read Noise 51
electrons
Full Well (ADC saturation)
~ 4 x 104
SNR 47 dB
Dynamic Range 70

18. Prague activity Calibration of MXRs for ATLAS 55Fe 6 KeV
241Am 50 KeV, 14 KeV
252Cf 2 MeV
AmBe 4 MeV
Results in numbers
16 MXRs calibrated with Am and Fe
1 in progress, 4 left
10 MXRs calibrated with Sr
4 MXRs calibrated with neutrons

19. Thank you for attention!

20. University of Glasgow, Scotland
1st - 5th September 2008
The conference explores the scientific and technical developments of detector systems used in: Astronomy and space science; Astrophysics; Condensed matter studies; Industrial applications; Life sciences; Medical physics; Nuclear Physics, Particle physics and Synchrotron based science.
National Organising
Committee
(subject to change)
P.P. Allport, Liverpool
R.L. Bates, Glasgow
A.J. Bird, Southampton
C.R. Cunningham, UK ATC, Edinburgh
G.E. Derbyshire, STFC, RAL
P. Evans, ICR, London
R. Farrow, STFC, Daresbury
W. Faruqi, MRC, Cambridge
M. Grande, Aberystwyth
P.R. Hobson, Brunel
D.P. Langstaff, Aberystwyth
P.J. Nolan, Liverpool
D.J. Parker, Birmingham
P.J. Sellin, Surrey
A. Smith, MSSL, London
R. Speller, UCL, London
T.J. Sumner, IC, London
S. Watts, Manchester

22. + - Radiation Metal layers Dielectric for insulation and passivation
Polysilicon N+ N+ P+ - + N+
P-Well
N-Well
P-Well
Potential barriers
Concept first proposed in 1999, and published in NIM in 2001 (R. Turchetta et al.)
P-epitaxial layer
P-substrate