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.
226Y.Matsunaga10.2.2FloatingSurfaceType
Analternativelow-noiseandwidedynamicrangechargedetectorcalled“double-gate oatingsurfacedetector”differsfromthe oatingwelltypeinthattheP-channelFETcurrent owsatthesilicon–silicondioxideinterface.Anadvantageofthistypeisitshighconversiongainduetothesmallsensingareacomparedtothe oatingwelltype.Thedeviceachievesacharge-to-voltageconversiongainof220 V/electronandadynamicrangeof79dBat3.58MHzvideobandwidthandatroomtemperature.Thisdetectorshowsaneffectivereadoutnoiseofonly0.5electronsrms,sothatitcanbeusedasanelectroncountingdetectorandtheevaluationcanbedonebydirectlyobservingthediscretelevelscorrespondingtothenumberofsignalelectrons.The79dBdynamicrangeissuf cientforaCCDimagesensordetector.
10.2.2.1DeviceStructure
ThedevelopedchargedetectorhaslowsensingcapacitanceandastructurewhichisinherentlyfreeofkTCnoise.Theprincipleisacombinationofann-typeburiedsensingchannelandaP-channelsurfacedetectiontransistoracrossit[5–7].Figure10.9showsacross-sectionalviewofthedetectiontransistoracrossthesensingchannel.Ashallowp-wellwithasensingchannelinitandsource/drainpCregionsareformedonann-typesubstrate.Theshallowp-wellunderasensingchanneliscompletelydepleted.TheP-typechannelforthedetectiontransistorliesatthesilicon–silicondioxideinterface.ThechargepacketsmodulatethechannelconductanceintheP-channeldetectiontransistor.
SGD
Sensing channel
Fig.10.9Crosssectionof oatingsurfacedetectiontransistor
