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박성근 : Sung-Kun Park, Ph. D, sungkun1.park@sk.com

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

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P12

1

P11

3

P13

4

P21 P22

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P23

6

P31

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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