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.
10Low-NoiseElectronicImagingwithDouble-GateFETs
Fig.10.10Practical oating
surfacechargedetector
structure227
Figure10.10showsapracticaloutputampli erfordetectingthecharge(electron)packetstransferredinathree-phaselinearCCD,whichisfabricatedinashallowp-wellonthen-typesubstrateof45 cmresistivity.ThepotentialcontrolgateGareawiththethickgateoxidelayermeasures4 4 m2whichissmallerthanthatofthe oatingwelltype.ThethingatelayerundertheFPPis120nmthickwhichisslightthickerthanthatofthe oatingwelltype.ToformtheP-typechannelforthedetectiontransistor,alocaldeepphosphorusimplantonthesensingchannelisrequired[3,7].Acharge(electron)packetistransferredintothesensingchannelthroughtheoutputgate(OG)atthefalltimeofa¥1clockvoltageappliedonthelasttransferelectrodeoftheCCD.Subsequently,itisconvertedtoavoltagesignalusingthe rst-stagesource-follower,whichconsistsofthedetectiontransistorandaloadtransistor.Thedrainofthedetectiontransistorisgrounded,andthesourcevoltageoftheloadtransistoris15V.ThevoltageappliedtothepotentialcontrolgateGisadjustedbetween30and 80V.Anoutputsignalisgeneratedusingthesecond-stagesource-followerconstructedwithn-channelMOStransistors.Toremovethecharge(electron)packetfromthesensingchannelregionintotheresetdrain(RD),apositivepulseisappliedtotheresetgate(RS).Thiscompletelydepletesthesensingchannelinaso-called“transferoperation.”Asaconsequence,thedetectorhasnoreset(kTC)noise[5,6].
10.2.2.2DeviceSimulation
Atwo-dimensionaldevicesimulator,handlingbothsignalelectronsinabulkpoten-tialwellandholecurrentalongthesilicon–silicondioxideinterfacesimultaneously,hasbeennewlydevelopedtoanalyzethe oatingsurfacedetector.Thesimulationsweredonealongthesignalelectrontransferdirection.Figure10.11a,bshowsthepotentialdistributionsfornosignalchargeandfor3600-electronsignalcharge,respectively.ThepotentiallevelatyD0inFig.10.11indicatesthesurfacepotential.The rstmaximumpotentiallevelalongtheyaxisindicatestheburied-channel
