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What Old Microwave Tricks Can Do in the New Nano Era?

What Old Microwave Tricks Can Do in the New Nano Era?. for semiconductor people of course. Yuen-Wuu Suen Department of Physics, National ChungHsing University 孫允武 中興大學物理系. OUTLINES:. What is so “NANO” in microwaves? What do people think of using microwaves?

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What Old Microwave Tricks Can Do in the New Nano Era?

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  1. What Old Microwave Tricks Can Do in the New Nano Era? for semiconductor people of course Yuen-Wuu Suen Department of Physics, National ChungHsing University 孫允武 中興大學物理系 1

  2. OUTLINES: • What is so “NANO” in microwaves? • What do people think of using microwaves? • What I am doing about microwaves and makes them kind of “nano”!! SCALES: time, length, energy Some novel thinking! Remember I am in the middle of Taiwan and between no where! 2

  3. FROM ELVA-1, RUSSIA http://www.elva-1.spb.ru/ (in vacuum) 3m 30cm 3cm 3mm 300mm 100MHz 1GHz 10GHz 100GHz 1000GHz About Microwaves: Frequency: about 1GHz~40GHz Sources up to about 1000 GHz are easily available! ---so called millimeter (submillimeter) wave! Wavelength: NOTHING NANO???? 3

  4. E 4×10-7eV 4×10-6eV 0.04meV 0.4meV 4meV E/kB 5mK 50mK 0.5K 5K 50K (in vacuum) (4.8) 3m 30cm 3cm 3mm 300mm 100MHz 1GHz 10GHz 100GHz 1000GHz Energy: Something I can never remember:h=6.63×10-34J·s =4.136×10-15eV·skB=1.38×10-23J·K-1=8.617×10-5eV·K-1 4

  5. 4×10-7eV 4×10-6eV 0.04meV 0.4meV 4meV E E/kB 5mK 50mK 0.5K 5K 50K Comparison Between Energy Scales Bandgap of semiconductors about 0.2~3eV Conduction-band or valence-band discontinuity about 30~900meV Energy of an optical phonon about 30~50meV Energy spacing for a electron in a typical quantum well (QW) about 30~100meV Fermi energy for electrons in a QW few meV Ionization energy of shallow donors or aceptors about 10~50meV Exciton binding energy about 5~30meV 100GHz 1THz 1GHz 5

  6. Some possibility here for quantum dots or low-dimensional systems Let’s talk about something related to microwaves E Free carrier absorption phonon EF photon k At low f (compared to 1/tscatter), it is just joule heating. try some numbers: 6

  7. Besides microwave radars, satellite communications, ovens…, what else microwaves can do? 7

  8. Electron spin splittings (electron spin resonance ESR) For free electrons g=2 f0(GHz)=28.0B(tesla) In semiconductors depend on host semiconductors and fields DE=g*mBB GaAs 0.44, GaN 1.98, InSb –51, Ge –2.5, Si 1.98 Let’s try electron spins and magnets!! The famous 21 cm line??? (If you know quantum mechanics very well, it comes from the hyperfine interaction. H=AS1·S2) H f0=1.42GHz Slower than your P4! 0.53Å Very “NANO”!! Radio Astronomy 8

  9. Cyclotron resonance B z fc(GHz)=28.0(m0/m*)B(tesla) For electrons confined in a two-dimensional interface Landau levels 9

  10. What can you do about the length scale? Why is it so long compared to “NANO”? The light travels so fast!! even divided by a reflective index. l=c/nf Then let’s translate it to something (somewave) slower. Maybe it will become more “NANO”. It comes out to be an acoustic wave. Or you want it on a surface, and then it should be a surface acoustic wave (SAW). cs~ 3000 m/s~ 10-5c 10

  11. f for EM of the same l as SAW 1013Hz 1014Hz 1015Hz 1016Hz 1017Hz E E 4×10-7eV 40meV 400meV 4×10-6eV 0.04meV 4eV 40eV 0.4meV 400V 4meV E/kB 5mK 50mK 0.5K 5K 50K (4.8) Let’s see the scales again! lSAW 30mm 3mm 300nm 30nm 3nm 3m 30cm 3cm 3mm 300mm 100MHz 1GHz 10GHz 100GHz 1000GHz 11

  12. First you need a piezoelectric substrate. Electric field Mechanical strain OR You must place an inter-digit (comb-like) electrode on the surface as a transducer. One can use optical or thermal methods---but less defined properties of SAWs. laser SAW heat SAW lSAW How to generate SAWs? You need an e-beam writer to get “NANO”. 12

  13. MORE about SAWs • A SAW on the surface of a piezoelectric substrate travels with a spatially modulated electric field, which gives a wave-like electric potential variation near the surface. • A SAW without an associated piezoelectric field is useless for microelectronics or nanoelectronics. For example, water wave. • The propagation properties of the SAW are very sensitive to the electrical or mechanical properties near the surface. Therefore, it is very useful for sensor applications. • The SAW is very useful on detecting the material properties of the length scale lSAW. • The SAW can provide a controllable electrostatic-like field in the scale of lSAW. Of course the distribution is flying. 13

  14. A SAW Delay Line as a Detector Almost anything changed here can be detected. You can build an oscillator including this SAW sensor, or you can hook up to an expensive vector analyzer to measure S’s. 14

  15. Anything GOOD to use SAW detectors?! • No contact! • Short wavelength compared to EM signals at the same frequency. • Low energy compared to EM signals at the same wavelength. • We can use SAWs to detect the special length scale in the sample via the size-resonance of SAWs and the sample. 15

  16. Besides those old goodies and odds, what’s new and “NANO”? Some thinking…….. 1. Make energy levels in nanostructures microwave active, so that one can use microwave doing something. 2. One can use SAW sensor to detect some nano features in nanostructures. 3. One can use SAW to drive electrons or holes to anywhere your want, where anywhere=nanostructures or quantum dots……. 16

  17. Microwave spectroscopy of a quantum-dot molecule T.H.OOSTERKAMP et al Nature395, 873 - 876 (1998) Photon resonances in a double-dot sample. The metallic gates (1, 2, 3 and F) are fabricated on top of a GaAs/AlGaAs heterostructure with a two-dimensional electron gas (2DEG) 100 nm below the surface. Measured pumped current through the strongly coupled double-dot. 17

  18. Determination of the complex microwave photoconductance of a single quantum dotH. Qin, F. Simmel, R. H. Blick, J. P. Kotthaus, W. Wegscheider, and M. Bichler Phys. Rev. B 63, 035320 (2001) Amplitude |A|of the photoconductance measurement obtained with the two-source setup. Bias dependence of the quantum dot conductance in the vicinity of a single resonance. Energy level alignment. 18

  19. Experimental setup for the two-source measurement:Two millimeter waves with a slight frequency offset generated by two phase-locked microwave synthesizers ( f =18.08 GHz and df =2.1 kHz) are added, doubled and filtered. You can see some old microwave goodies in their setup. 19

  20. Single-electron acoustic charge transport on shallow-etched channels in a perpendicular magnetic field J. Cunningham et alPhysical Review B 62, pp. 1564-1567 (2000) fSAW=2.716 25 GHz, I=nefSAW They are trying to make a new electric current standard. 20

  21. Flying potential and flying electrons 21

  22. Quantum computation and spintronics Quantum computation using electrons trapped by surface acoustic wavesC. H. W. Barnes, J. M. Shilton, and A. M. Robinson Physical Review B 62, pp. 8410-8419 (2000) (a) Schematic diagram showing the effective potential due to a SAW passing across a Q1DC; (b) potential through the center of (a), parallel to the Q1DC. 22

  23. A Flying Qubit quantum bit Spin separation!! Spin operation!! 23

  24. Toward a quantum computer a SAW quantum-gate network Controlled-NOT gate Probably you need to know some quantum mechanics before going any further!? 24

  25. Acoustically Driven Storage of Light in a Quantum WellC. Rocke, S. Zimmermann, A. Wixforth, J. P. Kotthaus, G. Böhm, and G. Weimann, Phys. Rev. Lett. 78, 4099 (1997); Let’s talk about something opto…. If I can drive electrons around, I think I can drive electrons and holes (or excitons) around. Then I want to select a place for them to recombine at the time I suggest…..and I want…. 25

  26. What will happen if I drive electrons and holes to a quantum dot ( laser if you want)? Or to an array of quantum dots (lasers)… or … (anything you can imagine) Photon trains and lasing: The periodically pumped quantum dotC. Wiele, F. Haake, C. Rocke, and A. WixforthPHYSICAL REVIEW A 58, 2680 (1998) Quantum-dot laser with periodic pumping C.Wiele et alPhysical Review A 60, pp. 4986-4995 (1999) 26

  27. What are we doing in NCHU? • We have build a type-II phase lock loop (PLL) for pulsed microwave signal to detect very small phase variations due to absorption of microwave or SAW signals by electron systems. The resolution of the phase is better than 0.01 degree with average of –100dBm input power.The sensor is SAW delay line or coplanar waveguide. • We are setting up a simple e-beam writer. • We are fabricating high-frequency SAW transducers. • We are trying to digging small “nano” holes. • We are making lots of microwave connection cables. 27

  28. RF or Microwave Generator (A) DC-Coupled Frequency Modulation (FM) Integrator 積分器 黑色:低頻訊號 橙色:高頻訊號 Directional Couplers (I) (B) (b2) (b1) Double-Balance Mixer (M) PLL Precision Counter (C) (b3) Pulse Generator (P) High Speed Diode Switch Power Splitter (S) Time Delay Gated Average (s2) (s1) (D) (H) Power Detector (J) Step Attenuator Amplifier (E) (G) Intensity Output Stainless-Steal Semirigid Coax Stainless-Steal Semirigid Coax SAW Receiver IDT SAW Emitter IDT Sample Z Z (F) (F) Impedance Match Network Impedance Match Network Active LDES Region Cryogenic Environment Pulsed RF/Microwave PLL and Gated Averaging System • Why pulsed? • Use low average power to prevent from heating • Use gated averaging technique to avoid direct EM interruption • Avoid the reflection and multiple reflection signals What’s different from others: We use type II PLL, home-brew sample-&-hold circuits, and cheap lock-in amplifiers. 28

  29. An improved homodyne amplitude detection scheme (if you still want to know some details, and still awake) Ref. Signal 0º 90º mixer To PLL 90º hybrid ~0 To amplitude detection Power splitter A home-made vector meter?? Signal from the sample 29

  30. s1(t) s2(t) signal of mixer or power detector time delay s4(t) signal after SH Direct coupled EM Reflected signals sampling delay set by pulse generator s3(t) fed into lock-in sampling gate set by a pulse generatorfed into the controlling node of a sample-and-hold circuit Signal Gating & Averaging: ~200 ms set by lock-in amp Peak power about –30dBm s1(t) RF/Microwave pulse train 0.2~2 ms set by pulse shaping circuit 3~4 ms set by lock-in amp 30

  31. Our system is working------ Guess which one is the PLL system? 31

  32. A semiconductor chip attached on the SAW delay line Chip tied on the SAW delay line BeCu SR coax 5mm IDT SAW transducer He3 sample holder 32

  33. Detection by Phase Lock Loop (PLL) f0 =f1+ fs =b1l1+bs(B)ls Df0 =0=Df1+Dfs(B) =Db1l1+Dbs(B)ls fs=bsls PLL system phase=f1=b1l1 sample known Sample under detection B:the parameter (magnetic field) changed in the experimentu:velocity of the wave Dw can be measured very accurately. Type-II PLL 33

  34. Reference From sample Keep at a constant phase difference Reference Df From sample Due to the change of sample conditions Reference Tuning the frequency to match the phase From sample 34

  35. SAW Delay-Line Sensor L l GaAs:3.6×10-7W-1GaAs/LiNO3(Y-Z):1.8×10-6W-1 35

  36. Coplanar Waveguide (CPW) Sensor 50Wmeandering CPWtotal length ls Electric field 36

  37. Coplanar Waveguide (CPW) Sensor Some formulae: or 37

  38. Data read from SAW delay line f0=120MHzT=0.3KGaAs/AlGaAs 2DES ns=2.5×1011 cm-2 38

  39. Data read from CPW: 39

  40. More data: 40

  41. High frequency IDT pattern made by e-beam lithography Still, not “nano” enough! 41

  42. Time delay response of a pulse microwave input 42

  43. Phys. Rev. So-Called Flows ofMW modules, Graduate students, ……….. 43

  44. UnderConstruction^0^ 1. l<1mm e-beam writer 2. Acoustoelectric effect V or A spins 3. Quantum dots, spins, spintronics Nano…..Nano…..Nano…..Nano…..Nano…..Nano…..Nano…..Nano…..Nano…..Nano….. 4. Buying source of higher frequency, maybe to THz. 44

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