leiting pan, nankai university introduction to ccd, emccd, iccd the speaker: leiting pan the tutor:...

Leiting Pan, Nankai University

Introduction to CCD, EMCCD, ICCD

The Speaker: Leiting Pan The Tutor: Jingjun Xu


Principle of CCD

Parameters of CCD

ICCD and EMCCD

Content


1.Principle of CCD

1.1 Development of CCD

Fig.1贝尔实验室 George Smith 和Willard Boyle将可视电话和半导体泡存储技术结合发明了 CCD原型

Fig.2 现代 CCD芯片外观


1.2 Photoelectric Conversion

Incr

easi

ng e

nerg

y

Valence Band

1.26eV

Conduction Band

photon phot

on

Hole Electron

1.26eV 对应的波长为 1.12uM 。对于硅制成的光敏像元，在红端是穿透率过高，到达电荷存储区之前就已经发生复合，故量子效率下降；在蓝端则是由于辐射的穿透率差，加之芯片正面电极的反射和散射，量子效率也不高。蓝端探测效率的改进可以借助背面入射，并覆盖光学透明的荧光材料来实现。

Fig.3 silicon crystal have electrons arranged in discrete energy bands: The Valence Band and the Conduction Band.

1.Principle of CCD


1.3 Charge Collection

n p

Ele

ctri

c po

tent

ial

Potential along this line shownin graph above.

Cross section through the thickness of the CCD

e

Fig.4 the schematic diagram of electric potential of single pixel.

1.Principle of CCD


n p

Region of maximum potential

Ele

ctri

c po

tent

ial

pix

el

bou

nd

ary

pix

el

bou

nd

ary

inco

min

gp

hot

ons

Charge packetp-type silicon

n-type silicon

SiO2 Insulating layer

Electrode Structure

Fig.5 The schematic diagram of electron produce

1.Principle of CCD

1.3 Charge Collection


为实现电荷转移，通常使用电荷耦合的方法。传统做法是三相 CCD ，即每 3 个电容中只有一个用于存储电荷，只要按一定规律依次改变各电极的电压，就可以实现电荷转移。

123

Fig.6 The schematic diagram of electrons transfer

positive potential

negative potential

1.Principle of CCD

1.4 Charge Transfer


123

+5V

0V

-5V

+5V

0V

-5V

+5V

0V

-5V

Time-slice shown in diagram

1

2

3

1.Principle of CCD

1.4 Charge Transfer


123

+5V

0V

-5V

+5V

0V

-5V

+5V

0V

-5V

1

2

3

1.Principle of CCD

1.4 Charge Transfer


123

+5V

0V

-5V

+5V

0V

-5V

+5V

0V

-5V

1

2

3

Charge packet from subsequent pixel entersfrom left as first pixel exits to the right.

1.Principle of CCD

1.4 Charge Transfer


123

+5V

0V

-5V

+5V

0V

-5V

+5V

0V

-5V

1

2

3

1.Principle of CCD

1.4 Charge Transfer


1.5 Charge Transfer of Area CCD

Fig.6 The schematic diagram of 2-D matrix structure CCD

1.Principle of CCD


Image area clocks

Store area clocks

Amplifier

Serial clocks

Image area

Store area

In the split frame CCD geometry, the charge in each half of the image area could be shifted independently. Now imagine that the lower image area is covered with an opaque mask. This mask could be a layer of aluminium deposited on the CCD surface or it could be an external mask. This geometry is the basis of the ‘Frame transfer’ CCD that is used for high frame rate video applications. The area available for imaging is reduced by a half. The lower part of the image becomes the ‘Store area’.

Opaque mask

1.Principle of CCD



A common analogy for the operation of a CCD is as follows:

An number of buckets (Pixels) are distributed across a field (Focal Plane of a telescope)in a square array. The buckets are placed on top of a series of parallel conveyor belts and collect rain fall(Photons) across the field. The conveyor belts are initially stationary, while the rain slowly fills thebuckets (During the course of the exposure). Once the rain stops (The camera shutter closes) the conveyor belts start turning and transfer the buckets of rain , one by one , to a measuring cylinder (Electronic Amplifier) at the corner of the field (at the corner of the CCD)

The animation in the following slides demonstrates how the conveyor belts work.

1.Principle of CCD



RAIN (PHOTONS)

BUCKETS (PIXELS)

VERTICALCONVEYORBELTS(CCD COLUMNS)

HORIZONTALCONVEYOR BELT

(SERIAL REGISTER)

MEASURING CYLINDER(OUTPUT AMPLIFIER)

1.Principle of CCD

1.5 Charge

Transfer of Area CCD


Exposure finished, buckets now contain samples of rain.

1.Principle of CCD



Conveyor belt starts turning and transfers buckets. Rain collected on the vertical conveyor is tipped into buckets on the horizontal conveyor.

1.Principle of CCD



Vertical conveyor stops. Horizontal conveyor starts up and tips each bucket in turn intothe measuring cylinder .

1.Principle of CCD



`

After each bucket has been measured, the measuring cylinderis emptied , ready for the next bucket load.

1.Principle of CCD



1.Principle of CCD



A new set of empty buckets is set up on the horizontal conveyor and the process is repeated.

1.Principle of CCD



1.Principle of CCD



Eventually all the buckets have been measured, the CCD has been read out.

1.Principle of CCD



Fig.7 The schematic diagram of read sequence of a CCD

1.Principle of CCD



1.6 Pinciple of signal Acquisition in CCD假设一个圆形像点直径略小于一个象素边长。如果像点处于一个物理像素的中心，则该像点占用一个像素来成像；如果像点在像素的四个顶角处，则需要占用四个象素来成像，强度被减弱，则不能真实反应原象。像点等于一个或者两个物理像素都不一定能获得真实的图像，不管是在中心还是顶角处。如果能覆盖超过三个物理像素，可以获得比较真实的图像。现在利用尼奎斯特（ Nyquist ）定理来做为信号的模数转为原则，则图像的再现就不需要依赖与象点与象素之间的位置关系。Nyquist 定理：也即是抽样定理，是工程师在模拟信号的数字化中遵循的原则。理想抽样时，只要抽样频率大于或等于模拟信号中最高频率的两倍，就可以不失真地恢复模拟信号。

1.Principle of CCD


Image CCD Recording Image CCD Recording

Cen

tered O

n P

ixel

On

vertex of Pixels


Fig.8 The schematic diagram of Thick Front-side Illuminated CCD

They have a low Quantum Efficiency due to the reflection and absorption of light in the surface electrodes. Very poor blue response. The electrode structure prevents the use of an Anti-reflective coating that would otherwise boost performance.

n-type silicon

p-type silicon

Silicon dioxide insulating layerPolysilicon electrodes

Inco

min

g p

hot

ons

625m

2.1.1 Quantum Efficiency -FI CCD

2.Parameters of CCD


Light enters from the rear and so the electrodes do not obstruct the photons. The QE can approach 100% .These thinned CCDs become transparent to near infra-red light and the red response is poor. But Very good blue response

n-type silicon

p-type silicon

Silicon dioxide insulating layerPolysilicon electrodes

Anti-reflective (AR) coating

Inco

min

g p

hot

ons

15m

2.1.2 Quantum Efficiency -BI CCD

Fig.9 The schematic diagram of Thinned Back-side Illuminated CCD

2.Parameters of CCD


The reflected portion is now reduced to :

In the case where the reflectivity actually falls to zero! For silicon we require a material with n = 1.9, fortunately such a material exists, it is Hafnium Dioxide.

With an Anti-reflective coating we now have three mediums to consider :

nt

Airni

nsAR Coating

Silicon

[ ]nt x ni-ns

2

nt x ni+ns

2

2

ns nt

2=

2.1.3 QE- AR Coatings

2.Parameters of CCD


2.1.4 QE-FI CCD and BI CCD

Fig.10 The graph compares the quantum of efficiency of a thick frontside illuminated CCD and a thin backside illuminated CCD.

2.Parameters of CCD


2.1.4 QE- Deep Depletion BI CCD

Ele

ctri

c po

tent

ial

40m

Fig.11 The schematic diagram of Deep Depletion BI CCD

Red photons are now absorbed in the thicker bulk of the device.

Fig.12 The graph shows the improved QE response available from a deep depletion CCD.

2.Parameters of CCD


1.Photon Shot noise (Ns)– Incoming photons follow poisson statistics– Given by the square root of the signal– Important when measuring small changes over a large background

2.Readout Noise (Nr)– Due to the preamplifier and electronics. Higher the speed, higher Nr– Important in measuring low light levels e.g. weak fluorescence

3.Dark Noise (Nd)– Thermally generated electrons in the absence of any light– Cooling minimizes this noise– Important when long exposures are required e.g., Luciferase imaging

4.Pixel response non-uniformity–This noise source can be removed by ‘Flat Fielding’, an image processing

technique

2.2 Noise

2.Parameters of CCD


Fig.13 The graph shows the total noise and the relation with detected number of photons.

2.Parameters of CCD

2.2 Noise-overall noise


2.2.3 Noise-dark current

Fig.14 The graph shows the dark current noise is depend on temperature.

2.Parameters of CCD


2.Parameters of CCD

2.2.3 Noise-dynamic range


2.3 Spatial Resolution For high resolution spectroscopy, we offer cameras with 13 μm pixel size; otherwise 26 μm pixel size is standard.

The higher resolution devices typically have slightly lower dynamic range and lower maximum signal to noise due the lower well capacities.

Fig.15 The picture shows the choice for pixel size.

2.Parameters of CCD


Fast cameras have higher read noiseSpeed also means available light is limited ：1000 frames per second means 1 ms worth of light per frame Smaller field of view

(ROI) BinningRead-out rateVertical clock speedComputer

Fig.16 The picture shows the frame transfer of CCD

2.Parameters of CCD

2.4 Time Resolution


Image area clocks

Store area clocks

Amplifier

Serial clocks

Image area

Store area

Opaque mask

采集速度 F/s A B C D 全帧Overlapped 133.69 106.84 31.37 31.37 31.37

Non －overlapped

72.89 66.67 26.65 26.65 26.65

2.Parameters of CCD

2.4 Time Resolution


2.5 Parameters of Andor EMCCD

2.Parameters of CCD


2.Parameters of CCD

2.5 Parameters of Andor EMCCD


3.1 Typical CCD ， EMCCD ， ICCD

CCD—Charge Couple Device

EMCCD—Electron Multiplying CCD

ICCD—Intensified CCD

Fig.17 Typical CCD 结构图

Fig.18 ECCD 结构图 Fig.19 ICCD 结构图

3.ICCD and EMCCD


Ultimate sensitivity: it is possible to measure single photons.UV extended spectral sensitivity down to 200 nm.The most important: an extremely short shutter.

3.2.1 Basics of ICCD Intensified CCD camera are equipped with one or more(cascaded) image intensifier(s) that are mounted in front of the CCD camera either fiber optically or lens coupled. The image intensifier is gateable and acts as fast shutter. Its gain is adjustable.

3.ICCD and EMCCD


Input window capable of transmitting light over the range near UV visible to near IR with gateable photo cathode deposited on its inner surface.Micro channel plate (MCP) to provide electron gain.Output window on which a suitable luminescent screen (phosphor) in deposited.

3.2.1 Basics of ICCD

Fig.20 ICCD 工作原理图

3.ICCD and EMCCD


Gating considerations

The intensifier gate is achieved giving a pulse combing from a high voltage module. The output level if the HV-pulse module is usually +50V to block the image intensifier and drops to –180V during exposure time . Due to this pulse shape photoelectrons escape the photo cathode only during ,i.e., the camera is only active during ， with the high conductivity of the photo cathode, allows the intensifier to be gated as quickly as 5ns.

tt

t

Gate on pulse+50V

-180V

3.2.2 Photo Cathode

3.ICCD and EMCCD


A typical MCP consists of about 10,000,000 closely packed channels of common diameter .The diameter of each channel is ~ 10 microns.Every electron entering a channel in the MCP collides with the channel wall and produces secondary electrons, produce further secondary electrons is an electron gain up to . The l/d parameter (length/diameter) of the channels determines the maximum gain. A typical value is l/d=40.

3.2.3 Micro Channel Plate (MCP)

Fig.21 ICCD 的 MCP结构原理图

86 10~10

3.ICCD and EMCCD


3.3.1 Principle of EMCCD EMCCD(Electron-Multiplying CCD) 技术，有时也被称作“芯片上放大增益” (On-chip multiplication) 技术，是一种全新的微弱光信号增强探测技术，广泛应用于天文学，物理影像及生命科学等微弱信号探测领域。 EMCCD 与普通的 CCD 探测器的主要区别在于其读出（转移）寄存器后又接续有一串“增益寄存器”，在增益寄存器中，与转移寄存器不同的是其中的一个电极被两个电极取代，其中电极 1 被加以适当的电压而电极 2 提供时钟脉冲，但该电压比仅仅转移电荷所需要高很多。在电极 1 与电极 2 间产生的电场其强度足以使电子在转移过程中产生“撞击离子化”效应，产生了新的电子，即所谓的倍增或者说是增益；每次转移的倍增倍率非常小，最多大约只有×1.01~×1.015 倍，但是当如此过程重复相当多次（如陆续经过几千个增益寄存器的转移），信号就会实现可观的增益—可达1000 倍以上。常规的探测器采用的放大原理是在数据读出后通过 AD 转换后实现，使得在信号放大的同时也将噪声信号放大，这就大大地制约了其帧频速度和灵敏度的提高。而EMCCD采用在读出寄存器中对信号进行放大的技术， AD 所转换的信号为电子倍增后的信号，也是就说 EMCCD 的电子倍增只是对信号进行放大，对读出噪声不会放大，从而大大提高了探测信号的信噪比。

3.ICCD and EMCCD


可实现单光子探测的科学级 CCD可变的、线性的增益控制芯片增益放大技术，超低温制冷，最大限度减弱暗电流噪声，无可比拟的信噪比。实现高速与弱光探测的结合两种读出模式

3.3.2 Advantage of EMCCD

Fig.22 EMCCD的增益效果图

3.ICCD and EMCCD


ICCD 通过光电阴极实现光电转换，峰值量子效率不超过 50% ；EMCCD采用 ccd 芯片，背照式峰值量子效率可达 90%ICCD 的微通道板和荧光屏降低空间分辨率； EMCCD空间分辨率只取决于象素大小，比 ICCD分辨率高，适合生命科学领域ICCD 增强器中有几百上千伏高压，高增益下引入较强信号（可能很弱）导致象增强器损毁； EMCCD没有这么严格的要求，尽量避免饱和ICCD 象增强器成本高，价格高，第三代 ICCD 进出口管制；EMCCD 相对较好ICCD具有纳秒级的门宽实现高时间分辨； EMCCD 只能实现毫秒级时间分辨

3.4 ICCD and EMCCD

3.ICCD and EMCCD


Fig.23 The ICCD of Lavision corp. Germany

Fig.24 EMCCD of Andor corp. U.K.

3.ICCD and EMCCD


成像体会— ICCD,EMCCD,LCSM,CCD pixel

在时间与空间极限探测上，鱼翅和熊掌不可兼得，需求是关键，合理

使用，有效搭配！

3.ICCD and EMCCD


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leiting pan, nankai university introduction to ccd, emccd, iccd the speaker: leiting pan the tutor:...

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