A Low Noise and High Sensitivity Image Sensor with Imaging … Workshops/2015 Worksho… ·  · 2015-08-11A Low Noise and High Sensitivity Image Sensor with Imaging and Phase-Difference

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A Low Noise and High Sensitivity Image Sensor

with Imaging and Phase-Difference Detection AF in All Pixels

M.Kobayashi, M.Johnson, Y.Wada, H.Tsuboi, T.Ono, H.Takada, K.Togo,

T.Kishi, H.Takahashi, T.Ichikawa, S.Inoue

Canon Inc., 70-1, Yanagi-cho, Saiwai-ku, Kawasaki-shi, Kanagawa 212-8602, Japan

Phone: +81-3-3758-2111, Fax: +81-44-520-3218

E-mail: [email protected]

Abstract

In this paper, we describe a device structure and

optical design for a CMOS image sensor with the

phase-difference detection photodiodes (PD) for an

autofocus (AF) function. This image sensor has a

pixel separated into two PDs by a PN junction. All

the effective pixels function as both the imaging

and the phase-difference detection AF (PDAF). We

have realized a low dark random noise (=1.8e- at

1PD, 2.5e- at 1pixel) and high sensitivity

(=78,000e-/lx sec at 1green pixel) image sensor with

the imaging and the PDAF functions in all the

effective pixels.

Introduction

Recently, image sensors with the PDAF function at

image plane has been developed [1], [2]. These

realize the AF function by arranging exclusive

pixels to detect the phase-difference. In these image

sensors, a pair of partially light shielded PD is

arranged in a part of pixel array. The focusing speed

is extremely fast in comparison with conventional

contrast detection AF. The sensitivity, however, is

degraded by the light shielding structure and

interpolation processing by neighboring pixels is

necessary for image generation [2]. Therefore, the

number of pixels for AF function is limited to avoid

the deterioration of image quality.

In this work, we developed an image sensor with

the imaging and the PDAF functions in all the

effective pixels without exclusive pixel for AF

function. All the effective pixels have two PDs each

to detect phase-difference in one pixel without

partially light shielding structure. Therefore, one

pixel works as one AF point, and the sum of two PD

outputs equals one pixel output.

Fig. 1: Principle of the PDAF function

Principle Fig. 1 shows the principle of the PDAF function.

Exit pupil of an optical lens and a PD of the image

sensor are in optically conjugate relation by on-chip

micro-lens (ML). Therefore, each pixel by separating

into two PDs has the pupil split function for the

PDAF function. A light flux which passes through a

right half of the optical lens is led to the PD-A (the

Page 2

PD at left si

of the optica

side).

Defocusing

between th

provided fro

image-B (th

The directi

image-B is

and the back

These mea

lens is drive

defocusing a

Fi

Fig. 2 show

pixel consist

ML and on

consists of o

transistors

signal line (

eight transi

is symmetri

60frames pe

driven simu

Fig. 3 show

The PD-A

junction. T

consist of t

using the

area is m

boundary

ide) and whic

al lens is led t

g amount is

he peak of

om PD-A gr

he image prov

ion of the pe

opposite bet

k focus state

an that in the

en to a just f

amount and t

ig. 2: Schema

Pixel A

ws the schem

ts of two sub

ne color-filter

one PD, one

for one sign

CSL), thus o

istors and tw

ically arrang

er second re

ultaneously.

ws the cross s

and the PD

The PN jun

the insulatin

PN junction

minimized, li

is reduced

ch passes thr

to the PD-B

s calculated

the image

roup) and th

vided from PD

eak shift of th

tween the fr

e.

e camera sys

focus instant

the direction

atic view of 2x

Architecture

matic view of

b-pixels, and

r (CF) each.

floating diffu

nal output a

one pixel cons

wo CSLs. A p

ged left and r

adout speed

section diagr

D-B are sepa

nction separa

ng materials

n separation

ight reflecti

and defec

rough a left h

(the PD at ri

from dista

e-A (the im

he peak of

D-B group).

he image-A a

ront focus st

stem the opt

tly by calcula

n [3 .

x2 pixels

e

2x2 pixels. O

has one on-c

. One sub-pi

usion (FD), f

and one colu

sists of two P

pair of sub-pi

right. To achi

, four CSLs

ram of the pix

arated by a

ation does

(e.g. SiO2).

n, non-sensit

ion at Si/Si

cts at Si/Si

half

ight

ance

age

the

and

tate

tical

ated

One

chip

ixel

four

umn

PDs,

ixel

ieve

are

ixel.

PN

not

By

tive

iO2

iO2

inte

shr

and

In

p-ty

low

pin

p-ty

loss

ligh

nois

W

tim

tran

the

Fi

dep

per

ima

sen

the

pos

the

Th

dep

PD

cas

sim

high

cas

sep

erface is decr

rinkage at Si

d defects incr

n addition, a

ype region f

wer than tha

nned PD. Th

ype impurity

s of the incid

ht is divided i

se and high s

Fig. 3: Cro

We performed

me domain (

nsient analy

curvature of

g.4 shows

pendence of

rpendicular g

age sensor su

nsor structure

e light inte

sition of the i

e ML curvatu

he figure als

pendence of

-A, PD-B an

e (b) (the rad

mulated QE o

her than the

e (c) (RC=5.3

parated PDs,

reased. It is

i/SiO2 interfa

rease [4], [5].

an impurity

for the PN

at of the surf

herefore, reco

y separation

dent light is m

into PD-A an

sensitivity im

oss section di

Optical D

a three-dime

(FDTD) opt

ysis device s

f the on-chip

the simu

f the light

green inciden

urface, supe

e diagram. A

ensity is st

incident light

ure.

so shows th

the quantu

nd the sum

dius of curva

of a two PD

e case (a) (RC

3 m) 55.1%. B

the sensitiv

reported tha

ace causes d

y concentrat

junction se

face region f

ombination

n region is lo

minimized. T

nd PD-B, as a

mage sensor i

iagram of the

Design

ensional finit

tical simulat

imulation to

ML.

ulated ML

intensity p

nt light ( =55

erimposed on

A dark color

trong. The

ht changes de

he incident

um efficienci

of the two P

ature (RC) is

s summation

C=3.3 m) 51.

By adding sig

vity is equiva

at band-gap

dark current

tion of the

eparation is

forming the

rate in the

ow, and the

The incident

a result, low

is realized.

e pixel

te difference

tion and a

o determine

curvature

profiles for

50nm) to the

n the image

means that

condensing

epending on

light angle

ies (QE) of

PDs. In the

4.3 m), the

n is 59.5%.,

.6% and the

gnals of two

alent to that

Page 3

of one PD st

The bottom

angle depen

in the posit

PD-A in the

below the ra

the case (b

range is wid

case (c) 24

image-A an

range of th

performanc

tructure.

mmost figur

ndence of the

tive angle re

e negative an

atio of 0.2 is

b), the angle

der than the

degrees. Th

nd the imag

he incident

e is improved

Fig. 4

Incide

re shows the

e QE ratio of

egion and ra

ngle region. T

compared in

e range is 2

e case (a) 21 d

hat wider ra

ge-B can sep

light angle

d. Similarly,

4: Simulated

ent light angl

e incident li

f PD-A to PD

atio of PD-B

The angle ran

n three cases

25 degrees. T

degrees and

ange means

parate at wi

e, and the

the angle ran

ML curvatur

le dependenc

ight

D-B

B to

nge

. In

The

the

the

ider

AF

nge

abo

the

is n

cas

deg

ima

ape

AF

ML

sim

sha

re dependenc

ce of the QE a

ove the ratio o

case (b), the

narrower tha

e of (c) 15 d

grees means

age-B is bet

erture). To re

performance

L with the

mulation of t

ape of the ML

ce of the light

and the ratio

of 0.2 near 0

e angle range

an the case o

degrees. The

the separat

tter at large

ealize both hi

e in the desi

e PDAF fu

the height,

L is required.

t intensity pr

o of PD-A and

degrees is co

e is 9 degrees

of (a) 10 degr

narrower ra

tion of image

er F-number

high sensitivit

ign of two P

unction, the

the curvatu

rofiles,

d PD-B

ompared. In

s. The range

rees and the

ange near 0

e-A and the

r (=smaller

ty and high

PDs and one

e accurate

ure and the

Page 4

Table 1 su

performanc

process is

Optical form

6.4 m. Nu

points are b

18.5M. Full

two PDs). S

source with

random noi

pixel (@gain

pixel (@60

60frames pe

Fig. 5 show

sensor. Chip

High grad

achieved by

image sens

detection AF

The autho

T.Kato,

A.Takabaya

of Canon In

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both 9.2M. N

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ise is 1.8e- a

n=32, RT). D

, one secon

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ws the packa

p size is 29.9m

de and high

y the low n

sor with ima

F in all pixels

Acknow

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J.Iwata,

ashi, I.Onuki

nc. for their co

s

ama, �Superi

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��Phase Det

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�Digital Cam

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n Devices Me

mmary

the specifica

image sens

oly 4Metal C

35mm. Pixel

ective pixels

Number of e

ty is 40,000e

78,000e-/lx s

er, one gree

at one PD an

Dark current

d). Maximum

th full pixel r

age photograp

mm x 21.6mm

h speed ima

noise and h

aging and p

s.

wledgement

ike to thank

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i and Y.Hara

ontribution to

iority of Imag

rt, 36.38 (201

tection Pixel B

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mera with Ph

nstitute of Im

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ers, 61.21, (1

xtremely-Low

eeting (IEDM

ations and

sor. Fabricat

CMOS proce

size is 6.4 m

and the PD

effective PDs

e- (@one pixe

s (@2,856K li

en pixel). D

nd 2.5e- at o

t is 50e- at o

m frame rate

readout.

ph of this im

m.

aging has be

high sensitiv

phase-differe

t

k K.Kawaba

ma, A.Ok

ada the mem

o this work.

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the

tion

ess.

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DAF

s is

el =

ight

ark

one

one

e is

age

een

vity

ence

ata,

kita,

mber

F

ase Detection

ge Sensor� to

ation and Tel

on Image Sen

ation and Tel

used by local

568.

OS Image Sen

E Internatio

Table 1: S

perform

Fig. 5: Packag

n AF�,

o Realize Hig

levision Engi

nsor�,

levision Engi

strain at Si/S

nsor with Hi

onal. IEEE, 2

Summarized

mances of thi

ge photograp

gh Speed Aut

ineers, 65.3 (2

ineers, 68.3 (2

SiO2 edge�,

igh Saturatio

011.

specification

is image sens

ph of this ima

to Focus�,

2011): 290-29

2014): 203-20

on Capacity",

ns and

sor

age sensor

92.

07.

,