Charge coupled device (CCD)

Presented By:Darshil Shah (IU1241090051)

Sachin Jain (IU1241090018)

Jainam Patel (IU1241090033)

Outline

Introduction

Operational Mechanism

Surface-Channel charge coupled device (SCCD)

Dynamic characteristics

Application

Introduction

CCD is a array of MOS-diode structure that was proposed in 1969 by George smith & Willard boyle.

A charge-coupled device (CCD) is a device for the movement of electrical charge, usually from within the device to an area where the charge can be manipulated

The CCD/CTD can move the charges in the MOS diode along a predetermined path under the control of clock pulses

Types of CCD’s

SCCD (Surface channel CCD)

BCCD (Buried channel CCD)

JCCD (Junction CCD)

SCCD/BCCD stores and transfer the charges on the surface/interior of semiconductor respectively.

JCCD stores and transfer the charge packet at the PN-junction.

Operational Mechanism

Under control of externally applied gate voltage ,the potential wells and the charge packets can be shifted from one well to adjacent one rapidly through entire CCD structure.

Three operational mechanism allow the charge packets to move

1) Self –induced drift

2) Thermal diffusion

3) Fringing field drift

Energy band of MIS diode

Three-phase structure

Store and transfer of charger packet

SCCD

A surface channel CCD is basically an MOS diode structure. Its energy Band diagram is shown in figure. b and c. There are two cases for the creation of a charge packet under deep depletion

Case I: Zero Signal Charge(Qsig=0)

Gate voltage and surface potential are related by

Here Vfb =flat band voltageVi =voltage across the insulator Hence We obtain :

Case II: Stored Signal Charge(Qsig>0)

Surface Potential equation is given by :

The maximum charge density that can be stored on an MOS capacitor is approximately given by :

DYNAMIC CHARACTERISTICS

Charge transfer efficiency(ƞ) is defined as the fraction of charge transferred from one well to the next in a CCD .The fraction left behind is the transfer loss(Ɛ)

If a single charge pulse width an initial amplitude (Po) transfer down a CCD register after n transfers(phases), the amplitude (Pn) becomes

The maximum achievable transfer efficiency depends upon two factors:

1. How fast the free charge can be transferred between adjacent gates

2. How much of the charge gets trapped at each gate location by stationary states

Frequency Response: There are upper and lower frequency limitation for CCDs. The maximum frequency is limited by the channel length L.

Power Dissipation per bit is given by

Application

Photocopier

Bar-code Reader

CCTV cameras

Video cameras

Photographic cameras

Signal processing : The CCD can perform several analog and digital signal processing function such as delay, multiplexing, demultiplexing, transversal filtering, recursive filtering, integration, analog memory, digital memory and digital logic. Thus CCD are being used widely in special application for the very large scale integration (VLSI) circuit.

Infrared detection and imaging : CCD is capable of detecting and imaging the infrared light from a target by forming charge packets that are proportional to light intensity of target. These packets are shifted to detector point for detection, read-out, multiplexing and time and delay integration(TDI)

References

Semiconductor devices: Physics and technology, 2nd

Edition, Wiley India Edition, By S M Sze

Microwave devices and circuits, 3rd Edition ,PHI , By Samuel y. Liao.

http://hyperphysics.phy-astr.gsu.edu/hbase/solids/fermi.html

http://ecee.colorado.edu/~bart/book/flatband.htm