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박성근 : Sung-Kun Park, Ph. D, [email protected]
2000 ~ 2006 : 0.35um embedded Flash MCU0.18um Single Poly, 0.25um VST cell, 0.15um MROM
2006 ~ 2010 : 0.18um~90nm standalone Flash0.13um SONOS eFlash cell
2010 ~ 2015 : 90nm~40nm CIS OTP, 0.18um PMIC, SONOS / Single Poly eFlash cell
2016 ~ 2018 : 40nm 1.0um / 0.9um Pixel 2019 ~ : SKHU 전임 강사
US patent : ~ 50ea Paper & Conference : ~16ea IMW 2019 & IISW 2019
IEEE Electron Device Society Senior Member : 2016~
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Introduction
a. 5 Senses of Human
b. Image Sensor Application
c. Eye vs. Sensor
d. History of Image Sensor Technology
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Most important Sense of human
Smell Touch
Taste
Sight
Hearing
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Applications of CIS are increasing
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Image Sensors vs. Human eye
Film
Light sensing cell
Camera 덮개
렌즈
Iris
Retina
Image Sensor
Cone : ~2umRod : ~10um
Blind spot
lens
cornea
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Image Sensors vs. Human eye
[eye] [Optic nerve]
576M pixel@still 5M pixel@moving
Vs.
20cm
Dual camera 24Mpixel~1um
Wide dynamic range
speed1000m/s
shutter1/10000
~100000 sec
250M pixel~10um
0.64M pixel 1990
UV~IR
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History of Image Sensor
Voyager 1, 2
CCDAT&T Bell Labs @1969
CISJPL, Cal. Tech@1993
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• Birth of CIS, 1995• Innovation company
: Photobit• acquire by Micron, 2001• Micron CIS #1, 2005
• From FSI to BSI, 2008• Innovation company: OmniVision
• OVT iPhone supply
• From 2D to 3D Stack, 2012• Innovation company
: Sony• iPhone supply• Sony CIS dominate
What is next innovation ?
Technology Trend of CIS
• Light path ↓• FF ↑, Sensitivity ↑
+ ISP function ↑
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Structure of CIS
a. CIS in Smartphone
b. Module & Sensor
c. Structure of CIS
d. From FSI to multi-stack CIS
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DDI(Display Driver IC)
+TSC
(Touch Screen Controller)
CIS
Li-ionBattery
RFIC
AP
FlashDRAM
Fingerprint sensor
LCD + Touch Panel
PMIC
Smartphone : Display+ Semiconductor + Battery
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CIS Chip
CIS Module and Image Sensor
○ CIS chip : Pixel Array, ADC, ISP
[Module]
[Camera @smart phone]
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Pixel Structure Analysis
Color filter
PD
GridAR/FEP
Pixel Transistor
~3umdeep
Isolation~1.4um@B-DTI
Metal
u-lens
...
Logic @ISP
u-lens
Unit Pixel
Shared Pixel Tr.
PD
DX SXRX
TX
OV16880@techinsight
Photodiode
Grid
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FSI vs. BSI?
- FSI : Front Side Illumination (전면 조사 방식)
- BSI : Back Side Illumination (후면 조사 방식)
Pixel Size Shrink Benefits of BSI
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Anti-Reflection Coating(AR)
• Reduction of light reflection using multiple reflection of inserted medium.
• Inserted AR condition : thickness (¼ of wave length), refractive index( )sl nnn 0
[Reflection without AR]
[Reflection with AR]
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u-lens & color filter
Low sensitivity /black and white
High sensitivity /black and white
High sensitivity /Color
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Bayer pattern Color filter & u-lens
[Color Separation by CFA] [Light Focusing by u-lens]
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D
F44.22 Rayleigh Criterion;
PD
PD PD
Pixel size ↓, diffraction ↑ Pixel Signal ↓, Crosstalk ↑
Solution ? New Optical structure required (BSI, DTI)
~
nmLight 700~400:
PD
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Pixel size ↓, diffraction ↑ Pixel Signal ↓, Crosstalk ↑
Solution ? New Optical structure required (BSI, DTI)
Pixel Size 2.25um 1.75um 1.4um 1.1um 0.9um
Diffr
act
ion P
att
ern
QEFSI 65% 50% 40%
BSI 70% 60%30%
(expected)
X-talkFSI 19% 20% 22%
BSI 18% 24% 30%
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From FSI to Multi Stack Technology
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BSI vs. Stack BSI
TSV interconnection: Through Silicon Via
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Wf upside down and removal of substrate on Photodiode.
On the Photodiode, CFA & u-lens are located, Metal lines are below the PD
Logic function wf as a Handling wf @stack technology
Poly & Metal Wiring
PhotoDiode
Silicon
MT1MT2MT3MT4
PhotoDiode
Silicon
PD Formation
PhotoDiode
Silicon
MT1MT2MT3MT4
HandlingSubstrateOr 하판
PhotoDiode
MT1MT2MT3MT4
Flip & Bonding Thinning DTI & FEPformation
HandlingSubstrateOr 하판
CFA & MicrolensFormation
PhotoDiode
MT1MT2MT3MT4
CFA
Microlens
HandlingSubstrateOr 하판
PhotoDiode
MT1MT2MT3MT4
HandlingSubstrateOr 하판
DTI
FEPGrid
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Quantum Efficiency : The ratio of detected photon in expected pixel
Photon → CF (R,G,B Color Filter) → Photodiode
0
10
20
30
40
50
60
70
80
400 450 500 550 600 650 700
QE
(%
)
Wave Length (nm)
Blue X-talk Green X-talk Red X-talk
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Grid & B-DTI : Color Signal Separation
X-talk suppression @B-DTI
Color filter
PD
Pixel Transistor
Isolation~1.4um@B-DTI
Grid
Spatial crosstalkSpectral crosstalkElectrical crosstalk
High A/R DTI depth~1.5um
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Grid & B-DTI : Color Signal Separation
Si interface
IL-SiO2
Dangling bond curing: Field Effect Passivation
: Damage ↑ & Dark current/Hot PX↑
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Operating Principle of CIS
a. Si vs. Light
b. Color Sensing
c. Digital vs. Analog
d. 4T Structure Pixel Operation
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Si & Light ?
𝜈 =𝑐
𝜆
𝐸 = ℎ𝜈
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Absorption of Light
Ev
Ec
𝐸 = ℎ𝜈 > 1.12𝑒𝑉
Bandgap of Si
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Color ? : Bayer pattern
B Gb
Gr R
B Gb
Gr R
G G GB B
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Utilization of Si Absorption characteristic
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Digital vs. Analog : NAND Flash Memory Cell vs. CIS Pixel
code0 1023
△volt
Digital data
Controller
Storage
Digital
black
white
ISP
Analog(light)
Image
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1. Microlens : Optical collection of photons
Real Image
Bayer Image
Sensor Image
2. Color Filter : Wavelength(Color) separation
3. Pixel Array
1) Photodiode : Conversion of photons to
electrons
2) Pixel Amp. : Charge to voltage conversion
4. CDS : FD non-uniformity removal
5. ADC : Voltage to digital bit conversion
6. ISP : Raw image reconstruction
1) AWB, AE, Color interpolation
2) Noise reduction, Dead pixel Correction
Signal Path : from light to code
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Unit Pixel : Layout & Schematic
FD
DX
SXRX
TX
PD
FD
RXTX
SX
PD
VB2
VB1
sx_b
RX
SX
TX
VSSPX
VDDPX
VDDPX
VSSPX
ADC
FD
FD
VoutVdd
<Layout> <Schematic>
DX
Gate Purpose
TX Transfer
RX Reset
DX Source Follower
SX Select
△Q=C×△V
Vss
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Pixel Operation Sequence : How to operate Pixel
PD Reset Integration FD Reset Signal
FD
RXTX
SX
PD
VB2
VB1
sx_b
RX
SX
TX
VSSPX
VDDPX
VDDPX
VSSPX
ADC
FD
SX
RX
TX
PD Reset Integration Readout Idle Flush
FD Reset
Signal
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PD (Photodiode) Unit Pixel Pixel Array
~3um depth remain EPI PD (Photodiode) + ~10 PD & ~10 isolation implant
4T Pixel : PD + TX(Transfer)+RX(reset)+DX(Source Follower)+SX(select)
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Photon Transfer Curve
ILLUMINANCE (Lux)
PIX
EL O
UTPU
T (
mV)
0
dark level (mV/sec);temperature dependent
slope=sensitivity (mV/lux sec);wavelength dependent
Saturation level (mV);limited byPD & FD Capability, Pixel Amp Range, ADC Range …
noise floor;dark shot noise, Amp noise, ADC noise …
Photon shot noise;(noise electron) = (signal electron)1/2
SFGCEQE
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Image Signal Processing (ISP)
a. Demosaic : Color Interpolation
b. CCM : Color Correction Matrix
c. BLC : Black Level Correction
d. DPC : Dead Pixel Correction
e. LSC : Lens Shading Correction
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Demosaic : Color interpolation
Remaining pattern interpolation & data filling
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Color Correctionreference color chart Color correction matrix generation
Off-Diagonal : X-talk
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BLC (Black Level Compensation)
output
t
BLC Value
output
t
Base noise level removal Black level Output = Input – BLC Value
APS
Masked Pixel Array(Optical Black Pixel)
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DPC (Dead Pixel Correction)
Image correction by ISP algorithm
2
P12
1
P11
3
P13
4
P21 P22
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P23
6
P31
7
P33
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P32
ISP
OTP
Adjacent
Dead Pixel
X,Y
Before After
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LSC (Lens Shading Correction)
Lenz Shading
Shading Gain
edge vs. center area illumination value difference data is stored at OPT or EEPROMOutput = Input * LSC_Coeff (x, y);
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Other Application & Future Trend
a. Biometric
b. Depth
c. Surveillance
d. Global Shutter
e. High Sensitive
f. Future Trend
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Biometric Technology
iPhone X
Galaxy note S7 다양한 phone기본 적용
Iris recognition
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Depth Sensor
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Surveillance : Low light sensitive sensor
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Rolling shutter : moving image distortion due to sequential scanning.
Global Shutter : charge stored at additional storage node at the same time
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High Sensitive Photodiode
Avalanche Photon Diode (APD) Single-Photon Avalanche Diode (SPAD)
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Yole, CMOS Image Sensors
Various image application 3D sensor will immerge near future
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EOD