Progress Towards Active Pixel Sensor Detectors for Solar Orbiter Dr Nick Waltham
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Transcript of Progress Towards Active Pixel Sensor Detectors for Solar Orbiter Dr Nick Waltham
Progress Towards Active Pixel Sensor Detectors for Solar Orbiter
Dr Nick Waltham
Head of Imaging Systems Division,
Space Science & Technology Department, Rutherford Appleton Laboratory
CCDs for Solar Physics . . .
CCDs for Solar Physics e.g. SOHO, SMEI, SOLAR-B, STEREO . . . Future missions e.g. SDO
But inherent limitations . . . External drive electronics needed. Solar physics community always want more
pixels, more channels, faster readout. But with smaller/lower size, mass, and power !
And for Solar Orbiter . . . Radiation damage !
Protons, neutrons, etc Loss of charge transfer efficiency !
Pixel Size ? Smaller pixels yield a smaller instrument.
STEREO CCD
Solar Mass Ejection Imager (SMEI)
RAL - Current programme . . .
SMEI (Solar Mass Ejection Imager) CCD camera
Birmingham University, UCSD, AFRL, Primary requirement - high dynamic range. Await launch
STEREO/SECCHI solar science mission
CCD camera design for 4 instruments with NRL and Birmingham.
Key requirements - high speed readout, high dynamic range, yet reduced size, mass, and power.
Now feeds into camera designs for SDO AO proposals.
R&D Activities
ASIC based CCD camera readout electronics. CMOS Active Pixel Sensors.
Solar Mass Ejection Imager (SMEI)
CCD ASICsActive Pixels
What are we doing about it ?
An alternative sensor technology to CCDs . . .
Development of
Science-grade
CMOS Active Pixel Sensors !
What is an Active Pixel Sensor (APS) ?
RampGen
PixelArray
Counter
FiniteState
Machine
ColumnAmplifiers
ColumnComparators
Digital Output
Digital Latches
Digital Store
Pixel
Column Select
RowSelect
Reset
Photodiodes
Reset Voltage Vdd
SourceFollower
Image sensor with pixels. Wavelength coverage same as a CCD. Difference charge sensed inside pixel .
Advantages . . . CMOS allows on-chip readout circuitry. Low mass, low power cameras. Smaller pixel size.
Shorter optics / smaller instrument.
Charge sensed inside pixel . . .
No charge transfer.
Greater radiation tolerance.
What are we doing about it . . . Science-Grade APS development Program.
RAL APS Development Programme 1999 Design / modelling of pixel test structures (0.5 and 0.7 m CMOS).
2000 Fabrication and testing of pixel test structures. Established formal collaboration with Marconi (EEV)
Exchange of designs / ideas, packaging, testing, Back-thinning Unique capability !
Design of 512 x 512 pixel sensor (0.5 m CMOS)
2001 Fabrication of 512 x 512 pixel prototype sensors. Birmingham join collaboration (Helen Mapson-Menard, Chris Eyles). EEV thinning test structures and 512 x 512 prototypes. First tests of 512 x 512 prototypes. Planning for Solar Orbiter (move to 0.25 m CMOS).
2002 Design / fabrication of 0.25 m CMOS 4kx3k 5m pixel APS. Full testing of front and back-illuminated 512 x 512 prototypes.
RAL APS test structure development
Pixel Design Test Structure chip with four 16 x 16 pixel arrays
Test Results
QE ~35% 10um active thickness Noise estimate < 50 electrons rms Calculated node capacitance = 18 fF Overall responsivity = 6 V per electron Peak output signal = 1 volt (167k electrons) Dark signal = 140 mV per second (0.6 nA/cm2) Fixed pattern noise = 10mV pk-pk
Quadradot Pixel Quantum Efficiency
Helen Mapson-Menard Chris Eyles (Birmingham)
512 x 512 Pixel Prototype Pixel Active Pixel Sensor
6 inch wafer of 512 x 512 sensors
Wire-bonded to an evaluation PCB
Individual
512 x 512 pixel
APS chip
512 x 512 Pixel Prototype Pixel Active Pixel Sensor
Two test Images
512 x 512 Pixel Prototype Pixel Active Pixel Sensor
Note Dynamic range and Anti-blooming Performance !
So where next ?
ESA’s Solar Orbiter
Driven by the proposal of a Spectrometer on Solar Orbiter
Detector Requirements
EUV sensitive
Large format (4k x 4k pixels)
Small (5 m pixels)
Science-grade linearity, low-noise, good uniformity
Radiation hard
Low power
Solar Orbiter Detector
Foveon's 16.8-million-pixel APS
RampGen
PixelArray
Counter
FiniteState
Machine
ColumnAmplifiers
ColumnComparators
Digital Output
Digital Latches
Digital Store
Detector Goals 4k x 4k pixel sensor 5m pixel size 14 bit dynamic range EUV Sensitive 4-transistor CDS pixel 0.25 m rad-hard
CMOS process
Development Programme Refine requirement specification Develop CAD models and simulations Define architectural design Design, fabricate, and test 5m pixel test structures Transfer 14-15 bit ADC to 0.25 m CMOS Investigate back-thinning with Marconi
Demonstrate feasibility in time for the AO !
It can be done !
Solar Orbiter Detector - Photodiode pixels.
Standard APS pixel SO 4T pixel
Column Output
Ibias
Column Select Switch
Reset Switch
Source Follower
Input MOS
RST
SEL
Column Output
Ibias
Transfer Gate
RST
SEL
TX
Simplest architecture.
No kTC or Fixed-Pattern noise reduction.
kTC and Fixed-Pattern noise reduction
possible by differential readout of dark
and signal level.
Solar Orbiter Detector - Photodiode pixels.
4-MOS transistor pixel. PMOS transfer gate for kTC / FPN noise reduction and increased dynamic range.
Schematic Layout
Solar Orbiter Detector - Chip Architecture
PIXEL SELECTION LOGIC
4K x 3K PIXEL ARRAYDIFFERENTIAL ANALOGUE OUTPUT
DIFFERENTIAL AMPLIFIER
A
Solar Orbiter Detector - Progress
1. Area sensor: ESA’s Solar Orbiter for
EUV imaging of Sun 4Kx3K, noise
~ 10 e- rms, DR ~ 12+ bits
2. Linear sensor: TOPSAT-2
BNSC Earth Observation 1 m
ground resolution, colour, on-chip 10-
bit ADCs, ~ 1500 fps
3. Electron sensor: HEP Vertex (Linear
Collider, RHIC upgrade, biomed)
intelligence in the pixel, fast readout
(50MHz/row), low noise (~ 10 e- rms),
data sparsification, radiation
resistance
0.25 m CMOS manufactured by TSMC
IC design / manufacturing sharing reduction of costs
Linear sensor4,000 pixels at 3 m pitch
Electron sensor
Area sensor
4,000 * 3,000 = 12 Million pixels
5 m pitch
1
23
Solar Orbiter Detector - Progress
4k x 3k Sensor – Predictions from CAD simulation work
• Full Well Capacity ~ 46k electrons (5 m pixel)
• Readout Noise ~ 10 electrons rms
• Dynamic Range ~ 12+ bits
• Fill Factor ~ 30% (but be careful !)
• Readout rate ~ 1 MHz (through one port only)
• Readout time ~ 12 seconds (full-frame, no windowing)
Solar Orbiter Detector - Future
Future Possibilities
Chips of any format up to 4k x 4k (5 m) pixels. e.g.
4k x 512 (5 m) pixel strips on selected bands.
2k x 2k (10 m) pixels.
or you could have odd-shaped pixels (10 x 20 m).
CMOS allows you to design what you want !
Multi-port readout for higher frame rate.
Windowed readout.
Anything else wanted – besides EUV sensitivity ?
EUV sensitivity – Backthinning, or FIB, or ?
Two different approaches to enhance the EUV sensitivity of silicon APS.
1) Backthinning ( back-illumination): with Marconi Applied Technology
2) Front etching of the oxide by Focused Ion Beam
Front vs Rear illumination
Charge diffusion to adjacent pixelsIn field-free region
EUV Photon
EUV Photon
< 5m
Solar Orbiter Detector - Future
Development Programme
4k x 3k pixel Array Manufacture (Delivery Dec 02).
Array Packaging (Jan 03).
First light (Feb 03).
Testing of 512 x 512 pixel prototypes (front and rear illuminated). E2V are delivering thinned sensors this week.
Transfer of 14-15 bit ADC to 0.25 m CMOS in second phase.
Thinning of 4k x 3k pixel array and EUV testing.
Summary
Requirement
EUV Sensitivity
4k x 4k pixels
5 m pixel size
Readout < 1 second
Low power
Cooling
Radiation hardness
Availability
Science-grade CCD
Yes
Yes (for SDO ?)
No
Not easily
No
-80 °C
Poor (CTE degradation)
Soon (12 m pixels)
? (5 m pixels)
APS
Probably
Yes
Yes
Yes / Windowed readout
Yes
-80 °C
Good (no CTE involved)
(2003 – 2006) ?
Solar Orbiter Detector - Alternatives
Have considered naked CMOS APS so far.
Are there alternatives ?
Diamond / Bold ? Progress towards a large format array ?
Smallest pixel ? / Bump bonding ?
CID Radiation hard but limited availability, small range of
formats, large pixels, very high read noise.
Intensified APS – like in CDS ?