Single Event Effects in CMOS Image Sensors

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To cite this document: Lalucaa, Valerian and Goiffon, Vincent and Magnan, Pierre and Rolland, Guy and Petit, Sophie Single Event Effects in CMOS Image Sensors. (2012) In: 2nd Workshop on Radiation Effects in Optoelectronic Detectors, 27 November 2012 - 29 November 2012 (Toulouse, France). (Unpublished)

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Single Event Effects in CMOS Image Sensors

V. Lalucaa, V. Goiffon, P. Magnan,

ISAE, Image Sensor Research Team, Toulouse, France

G. Rolland, S. Petit

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Valérian Lalucaa – 28/11/2012 – Rad. Effects on Optoelectronic Detectors Workshop 2

Outline

Context and motivations

Results on peripheral circuits

Decoders

Readout circuits

Charge collection in pixels

Transient in pixels

Pixel saturation - Blooming

Total collected charge

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Context

CIS in space environment

Star tracker (STAR, HAS, …)

Scientific imagers (earth, sun, …)

Radiation effects

Cumulative (TID, DDD)

Single Event Effects (SEE)

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Valérian Lalucaa – 28/11/2012 – Rad. Effects on Optoelectronic Detectors Workshop

Motivations

SEE in CIS: Open questions

What kind of effect can be expected ?

Where ? What sub-circuit ?

Can they be predicted with an existing model ?

In this case, what are :

relevant simplifying assumptions?

model limitations ?

(6)

Several arrays tested

CMOS 0,18 µm

3T conventional photodiode

128 x 128 pixels

Heavy ions : N, Ar, Kr, Xe

Energy : 60 to 611 MeV

LET : 3,3 to 67,7 MeV.cm²/mg

Normal Incidence

Sensor area exposed

Digital conversion outside the sensor

Frame grabbing outside the sensor

Experimental setup

SEE from

the imager

only

Linear Energy Transfer

versus depth in Si

(7)

Results section : Outline

6

Results on peripheral

circuits

Decoders

Readout circuits

Charge collection in

pixels

Transient in pixels

Total collected charge

Pixel saturation

(8)

Decoders

Decoders X (Columns) and Y (Rows)

Standard CMOS

NMOS and PMOS Transistors

Parasitic Thyristor : Latch-up

TCAD Simulation worst case : no SEL

Experimental : no Single Event Latch-up (SEL)

Maximum LET 67,7 MeV.cm²/mg and 3,7x10

6

_part/cm²

Transient currents in transistor nodes

Single Event Transient (SET):

address jump

Address

jump

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Results section: Outline

8

Results on peripheral

circuits

Decoders

Readout circuits

Charge collection in

pixels

Transient in pixels

Total collected charge

Pixel saturation

(10)

Results on readout circuits

Readout Circuits diagram

Large NMOST- PMOST

distance

No Latch-up

Large capacitances

NMOSFETs

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Results section: Outline

10

Results on peripheral

circuits

Decoders

Readout circuits

Charge collection in

pixels

Transient in pixels

Total collected charge

Pixel saturation

(12)

Pixels

Frames acquired in dark

Rolling Shutter mode

Pixels

Charge collection

SET on final frames

Bulk

(13)

Pixels

Charge collection

SET on final frames

Simplified Timing diagram

(Rolling shutter):

If the ion strikes the array during:

the integration phase

_è

Complete ion track

12

Ion

strike

(14)

Pixels

Charge collection

SET on final frames

Simplified Timing diagram

(Rolling shutter):

If the ion strikes the array during:

The integration phase

_è

Complete ion track

The readout phase

_è

Incomplete ion track

Ion

strike

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Collected charge profile (X-cut):

Saturation and blooming

14

X-cut

Estimated profile of

carriers created by the

particle.

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Collected charge profile (X-cut):

Saturation and blooming

X-cut

Maximum charge

allowed in photodiode

reset

VDD

_RST

Out

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Collected charge profile (X-cut):

Saturation and blooming

16

X-cut

Photodiode

(PHD)

Deposited

charge

Phd Output

Voltage V

_PHD

PHD saturation

(blooming)

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Collected charge profile (X-cut):

Saturation and blooming

X-cut

Readout

chain

Photodiode

(PHD)

Deposited

charge

Phd Output

Voltage V

_PHD

V

_out

Readout chain

saturation

Pixel Output

Voltage

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Total collected charge

Total collected charge (sum of all the pixel values)

Difference between theoretical deposited charge and

measured value, due to :

Saturation (~80%) / Charge collection efficiency (CCE) (~20%)

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Charge lost by

readout chain

saturation

CCE<100%

Error bars : estimated loss due to saturation

Num

ber

of

collected

electrons

Ion and experiment

Recombination in SI

and surfaces

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STARDUST

1 _Software

Simulation software using

Simplified pixel array under ion irradiation

Model of ion track inside the device

Pixel model :

Depletion region

Drift model

Field-free region

Diffusion model

STI STI

Main differences

No transistors

No surface effects

T1 T2 T3

P doped substrate

N

Depl. region

No N-doped area

No saturation

Pixel

Simulation

Model

P doped substrate

Depl. region

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Data and simulation : Bulk substrate

Data and simulations on bulk substrates

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No Saturation

Simple model

Good agreement for

all ions

Xe

Kr

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Data and simulation : Epi. Substrate

Data and simulation on epitaxial substrates

Simulation poorly fit

the data.

Differences ?

• Delta electrons

• Recombination

• Bulk substrate

effect

(23)

Conclusion

CMOS 3T pixels exposed to heavy ions

No functional failure

SED: Addressing artifacts (SET in addressing circuits)

SEL: None observed (as expected in these devices)

Single Event Transient on pixels

Large differences between theoretical and measured charges

Attributed to the readout chain saturation (~80%) and the non ideal

charge collection efficiency (~20% of the discrepancy)

Simulation/Measurement comparison:

STARDUST (ideal sensitive volumes without surface effects)

P

redicts well the data, on

bulk substrate

Poor fit on thin

epitaxial substrate

(<10 µm)

Possibly due to surface effects (surface recombination, fill factor,

other collecting junctions (MOSFET drain & sources)…)

Future work

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