Abstract Virtually complete charge transfer can be achieved with charge coupleddevices(CCDs)intheburiedchannelconfigurationbecausetheburiedchannelCCDintroduces no transfer noise. However, conventional charge detectors incorporatedinto CCDs have a comparably large noise, which consists of thermal noise and 1/fnoisefromMOS transistorin theoutputchargedetectors.
224Y.
MatsunagaFig.10.6Potentialpro lesalongthedirectionperpendiculartodevicesurface.(a)Detectiontransistorwithonly1 mthickgateoxide(b)DetectiontransistorwithFPP
10.2.1.3Evaluation
Thedetectorwasevaluatedata7.16MHzclockfrequency,correspondingtotwicetheNTSCcolorsubcarrierfrequency.Thesignaldutyde nedbythesignaloutputperiodintheclockcyclewasapproximately70%,whichwasdeterminedbya40nspositivepulsesuppliedtotheresetgate(RS).Thecharge/voltageconversiongainofthedetectorwasmeasuredbyinjectingaseriesofchargesinapacketintotheCCDfromaninjectiondiodehavingacapacitanceofabout1fF.Thesizeofthechargepacketwascalculatedfromtheresetdraincurrent.Theresultantoutputamplitudewasobservedthroughanoscilloscope.Theoutputsignalbandwidthis20MHzunder7pFcapacitanceload.TheresultsofthemeasurementsareshowninFig.10.7Therelationbetweeninjectionchargequantityandoutputvoltageislinearoverarangeofchargepacketsfrom40to2,000electrons/packet,witharesponsivityof76 V/electron.Theoutputnoiseofthenewdetectorwasmeasuredusingaspectrumanalyzer.Figure10.8showsthenoisespectraofthedetector,bothinresetoperationandintransferoperation.Intheresetoperation,residualchargeinthesensingchannelincludesresetnoise(kTCnoise),chargeduetothermalnoisegeneratedinthechannelregionoftheresetgate(RS).Conversely,inthetransferoperation,nonoisechargeexists,becausethesignalchargeinthesensingchanneliscompletelytransferredintotheresetdrainbyapplyingapositivepulsetotheresetgate.The1=fnoisebelow2MHz,whichisobservedinthenoisespectrumforthetransferoperation,isgeneratedbythedetectiontransistor.TheoverallRMSnoisevalueinthetransferoperation,withinthefrequencyrangeof10kHz–3.58MHz,was64 Vrmsatroomtemperature.Thevalueforthe“ oatingsurfacedetector”withtheFPPstructure,whichisfabricatedonthesamesubstrateforcomparisonandisdescribedbelow,was84 Vrmsunderthesamemeasuringconditions.Thedifferenceinthenoisevaluesiscausedbythe1=fnoiseduetosilicon–silicondioxideinterfacetraps.AsshowninFig.10.7,thenewdetectorwithacharge/voltageconversiongainashighas76 V/electron,anoiselevelaslowas64 Vrmsanda70%signaldutyratio,achievesaneffectivereadoutnoiseaslowas1.2electronsrms.
