DEPFET Sensor with Intrinsic Signal Compression ... - MPG HLL

DEPFET Sensor with Intrinsic Signal CompressionDeveloped for Use at the XFEL Free Electron Laser RadiationSourceG. Lutz, P. Lechner,PNSensor GmbH, MünchenM. Porro, L. Strüder, G. De Vita,Max-Planck Institut für extraterrestrische Physik, MünchenAll at MPI Semiconductor Laboratory, Otto Hahn Ring 6, D81739 München, Germany11 th European Symposium on Semiconductor DetectorsWildbad Kreuth, June 7-11, 2009Wildbad Kreuth 2009 Gerhard Lutz, PNSensor GmbH 1

Introduction• Development initialized by requrements of experiments at the futureXFEL (X-ray Free Electron Laser) X-ray source in Hamburg• Time structure: bunches of 3000 pulseswith 200 fs duration and 200ns spacingevery 100 µs• Photon energy range 500eV to 20keV• Desired detector requirements:o Single photon detection capabilityo Very high dynamic range(10 4 photons of 1keV)o 5 MHz readout capability• Required measurement precision:o For low signal: good enough for distinction of single photon from noiseo At high signal: better than Poisson fluctuation of expected photons• Detector concept based on DEPFET (Depleted Field Effect Transistor)invented already 1985 with new modifications providing signal compressionand very high charge handling capacitance.Wildbad Kreuth 2009 Gerhard Lutz, PNSensor GmbH 2

DEPFET BasicsDEPFET (Depleted Field Effect Transistor) Principle• Structure: FET on fully depleted bulk• Function:• Signal charge collectedin potential minimum(internal gate) belowtransistor channel• steers transistor current• Clearing by positivepulse on clear electrode• Properties:• Combined function of sensor,amplifier and memory cell• Use as readout element in semiconductor detectors and• as building block of semiconductor pixel detectors.Wildbad Kreuth 2009 Gerhard Lutz, PNSensor GmbH 3

DEPFET propertiesCircularlinear•Charge collection by drift mechanism overfull wafer thickness•low capacitance ► low noise•Signal charge remains undisturbed by readout ► repeated readout possible•Complete clearing of signal charge ► no reset noise•Full sensitivity over whole bulk ► large signal for m.i.p.; X-ray sens.•Thin radiation entrance window on backside ► X-ray sensitivity•Charge collection also in turned off mode ► low power consumption•Measurement at place of generation ► no charge transfer (loss) ►Operation over very large temperature range ► no cooling neededWildbad Kreuth 2009 Gerhard Lutz, PNSensor GmbH 4

DEPFET with Intrinsic Signal Compression: PrincipleExample: linear geometry• Internal Gate (IG) extendsinto the region below thesource (S)• Small signal chargesassemble below the gate (G)channel region providing fullsteering of the transistorcurrent• Larger charges distributedbetween channel and sourceregions. Only a fraction ofcharge is effective in steeringthe transistor current• Result: non-linear currentchargecharacteristicsWildbad Kreuth 2009 Gerhard Lutz, PNSensor GmbH 5

DEPFET layout for XFELXFEL pixel cell• Very small DEPFET with• Small central drain• Short gate• Very large source• Internal gate extendingbelow source• Clear structure• Combine DEPFET withhexagonal drift diode• Geometry:• DEPFET diameter 100µm• Cell diameter 236µmWildbad Kreuth 2009 Gerhard Lutz, PNSensor GmbH 6

DEPFET SimulationXFEL pixel cell• Device Simulations• along radial direction from centredrain (r=0) to cell rim (r=118µm),wafer thickness 280µm.Simulationcut• Technology simulation (DIOS)providing doping profiles followedby• 2-D Device simulation (TESCA)providing potential distribution,electron- and hole concentrations,currents, and further quantities asfunction of applied voltages andtime.Wildbad Kreuth 2009 Gerhard Lutz, PNSensor GmbH 7

Static simulation: : PotentialFull simulation region:DEPFET at lower left•DEPFET regionWildbad Kreuth 2009 Gerhard Lutz, PNSensor GmbH 8

Dynamic simulation: : Charge collection and signal response• Compare charge collection and signalgeneration for photon interaction nearentrance window in centre position andclose to the rim.• DEPFET in common sourceconfiguration (drain current readout)with 77.5 µA drain current• Generated charge 1 fC corresponding to6250 e-h pairs or 23 photons of 1keV• Charge collection time25 ns for central interaction60 ns for rim position• Signal settling time almost equal indrain readout configurationWildbad Kreuth 2009 Gerhard Lutz, PNSensor GmbH 9

Simulation: Non–linearresponse and signal compression• Properties were tuned torequirements of XFEL requiringsimultaneously• single X-ray sensitivity downto500eV energy• and the capability to collect10000 photons per pixel.• A linear region up to ~1.5fC(corresponding to 35 1keVphotons) provides highamplification: 1,8 µA/fCcorresponding to 77nA/1keVphoton.• It is followed by a non-linear(signal compression) region.• Compared to linear extrapolationfrom the low signal region, areduction of a factor 20 in theoutput signal range is achieved.Wildbad Kreuth 2009 Gerhard Lutz, PNSensor GmbH 10

Simulation: DEPFET properties at working point• Working point chosen so as toachieve required properties atreasonable power consumption:Vdrain = - 3VIdrain = 78 µAWildbad Kreuth 2009 Gerhard Lutz, PNSensor GmbH 11

Simulation: Choice of readout configuration• Possibilities:• Drain current readouto Direct coupling of detector toelectronics• Source voltage readouto AC coupling to electronicso Simplifies task of electronics(no base current compensationneeded)o requires integration of couplingcapacitor and source resistorinto detectoro Brings significant complicationto detector fabricationo Slows signals down due tocapacitive output loadWildbad Kreuth 2009 Gerhard Lutz, PNSensor GmbH 12

From Pixel to MatrixDEPFET cell with two metal layers connecting• Source(S), Gate(G), Driftring (R1) kept atDC potentials• Clear (CL) and Clear-gate (CLG) withpulsed signalsDEFET matrix:• Every second columnhas cells mirrorimaged aroundhorizontal axis• Drains are connectedindividually bybump bonding toelectronics waferWildbad Kreuth 2009 Gerhard Lutz, PNSensor GmbH 13

Summary• The new DEPFET structure provides simultaneously• good energy resolution for small signals,• signal compression and• very high charge handling capacity.• Combined with a silicon drift diode it forms the basic cell of a pixeldetector to be used at the XFEL Free Electron Laser X-ray radiation source.• The high sensitivity for low signals allows• single photon detection and• Signal compression• strongly reduces the output signal range• still keeping the measurement errorfar below statistical fluctuations in the number of produced photons.• The detector simplifies significantly the task of the readout electronicsWildbad Kreuth 2009 Gerhard Lutz, PNSensor GmbH 14

SummaryTHE ENDWildbad Kreuth 2009 Gerhard Lutz, PNSensor GmbH 15