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HEMT

Electrical characteristics of HEMT

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HEMT

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  1. Course: Nanoelectronic Device Arpan Deyasi High Electron Mobility Transistor Nanoelectronic Device Arpan Deyasi RCCIIT, India 5/30/2021 Arpan Deyasi, India 1

  2. Problems in conventional transistor Arpan Deyasi Scattering between donors/acceptors and mobile carriers Nanoelectronic D Impurity scattering Device M.C High noise 5/30/2021 Arpan Deyasi, India 2

  3. Solution of problem Arpan Deyasi Separate the two Nanoelectronic How? Doping is done in one region and Mobile carriers will subsequently migrate Device into another region Process is known as modulation doping 5/30/2021 Arpan Deyasi, India 3

  4. Carrier separation Arpan Deyasi Ionized donors Metal Nanoelectronic Metal Free Device electrons Undoped AlGaAs buffer AlGaAs donor layer GaAs well 5/30/2021 Arpan Deyasi, India 4

  5. Structure Arpan Deyasi Source Drain Nanoelectronic n+GaAs n+ GaAs Gate Device n+ AlGaAs n+ AlGaAs Undoped AlGaAs spacer layer GaAs 2DEG Semi-insulating substrate 5/30/2021 Arpan Deyasi, India 5

  6. Characteristics of HEMT Arpan Deyasi mobility of free carriers are very high due to suppressed ionized impurity scattering which makes very low gate-to-source resistance Nanoelectronic Device carrier freezeout problem is not present at extremely low temperature because of electrons presence in a region of energy below donor levels in high bandgap material. So the device is treated as high-gain, low-noise one 5/30/2021 Arpan Deyasi, India 6

  7. Characteristics of HEMT Arpan Deyasi Using materials with higher conduction band discontinuity, large device transconductance can be obtained Nanoelectronic Because of smaller active channel, it can be operated at lower temperature Device 5/30/2021 Arpan Deyasi, India 7

  8. Materials used in HEMTs Arpan Deyasi GaAs: used in the first HEMTs Nanoelectronic GaN: an improvement upon the GaAs based HEMTs InP: used in some of the most advanced HEMTs Device 5/30/2021 Arpan Deyasi, India 8

  9. Band Diagram Arpan Deyasi qφb Nanoelectronic Device ΔEC qVG z=0 z=-ds z=-d z 5/30/2021 Arpan Deyasi, India 9

  10. Sheet charge Density Arpan Deyasi Φb: barrier height of Schottky barrier gate ds: spacer layer distance d: gate-to-channel distance Device Nanoelectronic ξ: electric field at the interface region of barrier ns: 2-DEG density 5/30/2021 Arpan Deyasi, India 10

  11. Sheet charge Density Arpan Deyasi From Gauss law Nanoelectronic   = qn b s dielectric of barrier region Device 5/30/2021 Arpan Deyasi, India 11

  12. Sheet charge Density Arpan Deyasi Poisson’s equation is barrier region Nanoelectronic ( ) qN z    = − 2 Device b −  −  d z d = ( ) N z N where s 0 D   sd z N z = ( ) 0 5/30/2021 Arpan Deyasi, India 12

  13. Sheet charge Density Arpan Deyasi Integrating Nanoelectronic z   d dz Device d dz q = −  − ( ') ' N z dz  ' ' = 0 z z b 0 z   d dz q = − −  ( ') ' N z dz  ' z b 0 5/30/2021 Arpan Deyasi, India 13

  14. Sheet charge Density Arpan Deyasi Further integrating Nanoelectronic −  −  d d q  = − Device −  = =  − ( ) ( 0) ( ') ' z d z d dz N z dz  − − b ds ds q V z − = − ) 0 − =  − − 2 ( ( ) d d N d d D s  b 5/30/2021 Arpan Deyasi, India 14

  15. Sheet charge Density Arpan Deyasi qN  = − = − −  2 ( ) ( ) V z d d d d D Nanoelectronic s b qN  Let’s define Device = − 2 ( ) V d d D p s b This is the necessary voltage to pinch-off the doped AlxGa1-xAs layer 5/30/2021 Arpan Deyasi, India 15

  16. Sheet charge Density Arpan Deyasi        = = − = − ( ) n V V z d b q b Nanoelectronic s p qd From band diagram Device  E q E q = − =  − + − ( ) V z d V C F b G 5/30/2021 Arpan Deyasi, India 16

  17. Sheet charge Density Arpan Deyasi where Nanoelectronic VG: gate voltage EF: Fermi level ΔEC: conduction band discontinuity Device 5/30/2021 Arpan Deyasi, India 17

  18. Sheet charge Density Arpan Deyasi         E q = + + −  n V V b C Nanoelectronic s G p b qd Let’s define Device  E q =  − − V V C off b p 5/30/2021 Arpan Deyasi, India 18

  19. Sheet charge Density Arpan Deyasi      = − n V V b Nanoelectronic s G off qd Device cut-off potential 5/30/2021 Arpan Deyasi, India 19

  20. I-V characteristics Arpan Deyasi Current in active region Nanoelectronic  W C ( )     = − − 2 0.5 0 I V V V V n D G Th D D L Device 5/30/2021 Arpan Deyasi, India 20

  21. I-V characteristics Arpan Deyasi ( )  − V V V In active region Nanoelectronic D G Th  W C ( )  − 0 I V V V n Device D G Th D L  W C dI dV = = 0 g V n D Transconductance m D L G 5/30/2021 Arpan Deyasi, India 21

  22. I-V characteristics Arpan Deyasi ( )  − V V V In saturation region Nanoelectronic D G Th sat  W C ( ) 2 = − 0 I V V V n Device D G Th D sat sat L  W C 2 = 0 g V n m D sat sat L 5/30/2021 Arpan Deyasi, India 22

  23. Differences between MOSFETs and HEMTs Arpan Deyasi HEMTs MOSFETs Nanoelectronic Operation in the UHF range (300 MHz-3 GHz) Device Operate in the microwave range (300 MHz - 300 GHz) Doped region is used as the channel Heterojunction is used as the channel 5/30/2021 Arpan Deyasi, India 23

  24. Applications Precision sensors Arpan Deyasi Next generation wired/wireless communication Nanoelectronic Advanced radars Power electronics Device 5/30/2021 Arpan Deyasi, India 24

  25. Areas to be covered in future Arpan Deyasi Reliability of GaN and InP HEMT’s are excellent at lower frequencies Nanoelectronic Reliability issues need to be resolved in GaN and InP HEMT’s at higher frequencies Device Failure mechanisms such as gate sinking, thermal degradation of ohmic contact, and charge trapping needs further investigation New structures need to be developed to reduce parasitic capacitance and address the failure mechanisms 5/30/2021 Arpan Deyasi, India 25

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