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In conventional CMOS image sensors, the pixels (sensors) and circuits (logic)

are formed on the same silicon substrate.

Like oil and water, this coexistence of two conflicting elements makes it difficult

to optimize their characteristics and also imposes other constraints.The "stacked CMOS image sensor 1", a new generation of the back-illuminated

CMOS image sensor, developed by Sony solves these problems in one stroke.

Stacking the pixel section and the circuit section enables compact size,

high image quality, faster speeds and flexible integration of versatile functions.

Through this technology, Sony has created functions that will enable

differentiation of final products to provide new ways of enjoying images.

Sony's Stacked CMOS Image Sensor SolveAll Existing Problems in One Stroke

The expectations that customers have of afinal product containing an image sensor canbe categorized into expectations regardingpixels and those regarding circuits. (Seefigure 1.)When i t comes to p ixe ls , cus tomersare looking for improvements in basicperformance such as pixel size, speed,sensitivity and high pixel numbers. Forexample, smaller pixel sizes make it difficultto obtain greater sensitivity. However, Sonythinks that image sensors should captureimages at 1 lx (moonlight) and has onceagain raised their basic performance goalsaccordingly.It is often said that customers demand a newapproach from image sensors that will allowdifferentiation of in the design of the finalproduct, for example, fun and ease of use.Some think that Sony as a leader in digitalimaging technology should make better useof its intellectual property (IP).

T h e r e i s a l s o a s t r o n g d e m a n d f o rcustomization.

Proposal for fun andease of use

Proposal for Sony's digitalimaging technology

Customization

Compact sizeFaster speedsHigher sensitivityHigher pixel numbers

Improvement in BasicPerformance

Pixel (sensor) Circuit (logic)

Pixel (sensor) Circuit (logic)

Inefficiencies causedby unnecessary logicprocessesConstraints in processline generationPerformance and costbarriers to customiza-tion

Incompatibility of imagesensor specific processesand standard logicprocesses

Sensor processconstraints

Expectations of Pixels andCircuits

Figure 1 Demands by Customers that Use Image Sensors in Final Products

Figure 2 Sony's Objectives as an Image Sensor Supplier

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Sony has set a goal to develop a "Super Reality" sensor thatsurpasses human vision to achieve high speeds and highpicture quality. The increasing popularity of smartphones meansa greater diversification of camera usage. Sony would like tospecify a new evolution axis of higher performance in additionto this evolution axis.Sony meets the customers' expectation for greater differentiationin final products with the stacked CMOS image sensor that hasthe superb mechanism to provide new ways of enjoying images.

Figure 3 Stacked CMOS Image Sensors, the Next Generation of Back-illuminatedCMOS Image Sensors

circuits will also have to be made accordingto the 65 nm process rule, which is a majorconstraint. Even if production is outsourcedto external foundry manufacturers, it is notpossible to select the ideal logic process.In addition, customization was problematicboth in terms of performance and cost.The arrival of the stacked CMOS imagesensor neatly solves all these problems.

In a back-illuminated CMOS image sensor,both pixels and circuits are formed on thesilicon substrate, which is reduced to a

ccor ng

nExceeding Hu V s onTowar s Super Rea ty

Beautyindustry Sensing

Health care

Learning

Data andinformation

Viewing

HDR

RGBW

Image Quality

SpeedHigh

Fun t ona ty

1. Effective use of the supporting substrate

2. A newconcept

Back-illuminatedCMOS image sensor

StackedCMOS image sensor

Supporting substrate

Supporting substrate

Pixel section

Circuit section Layerstructure

Pixel section

Circuit section

Layerstructure

Circuit section

Conventional Newly-developed

Complete separation of pixel section andcircuit section

Sony's Objectives as a Supplier

Two Concepts that ChangesConfiguration Considerably

A number of hurdles remains to be cleared tosatisfy these expectations and demands. (Seefigure 2.)

Firstly, the pixel and circuit manufacturingprocesses are as irreconcilable as oil andwater. For example, to improve the lightgathering efficiency of the pixels opticalwaveguides have been introduced. The dryetching process required to do this causesdamage to the silicon crystals and the pixelsection makes it necessary to follow it upwith an annealing process (heat treatment) torecover from this damage. From the point ofview of the circuit section, heat treatment ishighly undesirable since it changes transistor

parameters. As described above, pursuingpixel section characteristics when formingpixels and circuits on the same silicon wafermeans that you add a constraint to the circuitsection.Completely unnecessary from the point ofview of the circuit section, it is a processthat the pixel section needs. On-chip colorfilters, microlenses and other componentsare formed both on the pixel section and alsothe circuit section, after which everything isremoved. These kind of inefficiencies existbecause the same silicon substrate is used forforming both pixels and circuits.There are also constraints in process linegeneration. Sony currently uses the 65 nmprocess rule in IC manufacturing. Sincethe same silicon substrate is used for boththe pixel section and the circuit section, the

few m to take in light. As it is difficult totransport a substrate this thin, a supportingsubstrate is usually added to the side oppositethe light receiving surface (back side). Sincea difference in the coefficient in thermalexpansion between the different layerscould cause them to separate, the supportingsubstrate, like the chip, is also a siliconsubstrate.The supporting substrate also being a siliconsubstrate makes it a natural first step to use itas a circuit layer. (See figure 3.)As placing the pixels and circuits on thesame silicon substrate is a precariousapproach at best, it is a natural second step tocompletely separate the two.

Future Image Sensor Evolution AxesProvide new comfortable ways of enjoying images

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before delivering the product. The newCMOS sensor makes it easier to add newfunctionality to increase the shooting fun of

the end user.

l Advantages to FinalProduct Manufacturers

The stacked structure makes it possible toplace large circuits on small chips, whichfurther simplifies differentiation. Also, thetechnology enables use of cutting-edgeprocesses with chips having formed circuitsto speed up signal processing speeds andreduce power consumption. It also facilitatesdesign and improves design flexibility.

l Advantages to Sony

The new technology enables us to quicklyprovide digital imaging IP, a Sony strength,to increase productivity of the externalfoundry cooperative manufacturers and toquickly respond to customization requests.

In the following, Sony will describe the sizeof circuits and their process rules thatcan be placed on the stacked circuit section

of typically sized image sensors. Digitalstill cameras mainly use Type 1/2.3 CMOSimage sensors. If the 45 nm process rule can

be used for the circuit section, it will becomepossible to implement signal processingcircuits that equal the DSPs used in high-end digital still cameras. And even the 65 nmrule will make possible signal processing formiddle class digital still cameras.Type 1/3.2 image sensor processed accordingto the 65 nm rule could be incorporated in asurveillance camera. And if the 45 nm rulewere used, it would enable integration of asignal processing circuit large enough formiddle class digital still cameras.Secondly, how can the surface area bereduced by completely separating the pixelsection from the circuit section?Sony's Type 1/4 CMOS image sensors canthen be reduced by 30% and SoC CMOSimage sensors for mobile phones withcamera signal processing capability can bereduced by 40%. Although CMOS sensorsare generally thought to be larger than CCDimage sensors, stacked CMOS image sensorsdo not need any registers and can thereforebe 20% smaller. The configuration of thesensor makes it ideal for use in medicalcameras and other industrial applications.

Impact Provided by CompletelySeparated Stacked Layers

Circuit Scale and Compact Size

The following sections give a description ofthe advantages that stacked CMOS imagesensors can provide with regard to previouslydescribed expectations and issues. (Seefigure 4.)

l Advantages to End Users

Complete separation will prevent pixelsfrom constraining circuits making it possibleto freely select a process that leads to high

picture quality. This will dramaticallyimprove sens i t iv i ty and o ther bas icperformance factors.W i t h c o n v e n t i o n a l C M O S i m a g esensors, there was a time lag betweenthe development of Sony digital imagingtechnology and until that technology couldbe differentiated for a customer product.For example, if a customer required a newalgorithm from Sony for a signal processingIC that would be ready in two years forintegration into a product, that technology

would have to be close to completion now.However, stacked CMOS image sensorsallow us to perform development in stepwith the customer. At the final stage, Sonyintegrates new technology, or IP, into thecircuit section of the stacked structure

Improved camera performanceNew product value through timelyaddition of new functionsThe experience of a product that isfun and easy to use

Differentiation of functions in a compact formHigh speed and low power consumptionthanks to a cutting-edge logic processOffers ease of design and flexibility in makingimprovements

Full use of Sony's digital imaging technologyFlexible selection of ideal process logic throughoutsourcingSensors with higher picture quality that enablegreater productive capacityCustomization requests can be quickly addressed

Sony

End userFinal productmanufacturers

n Figure 4 Potential of Stacked CMOS Image Sensors

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SonyProposal: T woNewFunctions toEliminateCommonShootingErrors

Stacked CMOS image sensors can be used for work role-sharing with customer's DSP, store digital imaging IP in the circuit

section or enable flexible integration of customer developed functions. First we will introduce two new functions and what theymean in the evolution of the camera.

Sony's unique RGBW Coding functionenabling clear shooting in dark roomsor at night

HDR (High Dynamic Range) Moviefunction which enables brilliant colorsto be captured even in bright settings

The built-in "RGBW Coding" function which adds W(White) pixels to the conventional range of RGB (Red-Green-Blue) pixels has realized higher sensitivity,enabling high-quality shooting with low noise even in darkindoor or night settings.

While the addition of W (White) pixels improvessensitivity, it has the problem of degrading image quality.However, Sony's own device technology and signalprocessing realizes superior sensitivity without hurtingimage quality.

When a stacked CMOS image sensor supporting these two functions are integrated into asmartphone or other device, there is no need to change the signal processing of the device.

Type 1/3.06 stacked CMOS image sensor with approx. 13.0M effective pixel sSample shipments planned for June, 2012

Type 1/4 stacked CMOS image sensor with approx. 8.0M effective pixelsSample shipments planned for August, 2012

Products with bothfunctions are plannedfor shipment

Typically, when shooting with differing light levels, such asan indoor setting against a bright outdoor background, therecan easily be blocked up shadows for dark areas or blownout highlights for bright areas. Such phenomena are a resultof the combination of low-light and bright-light which have

different optimal exposure conditions in the same shot.This function reduces this by setting two different exposureconditions within a single screen shooting and conductsthe appropriate signal processing for the captured imageinformation under each optimal exposure condition. Thisprocess generates an image with a broad dynamic rangeand enables shooting of both the background and subjectmatter with brilliant colors even in a bright environment.

Conventional RGBmethod Normal movie HDR movie

Newly developed "RGBWCoding" method