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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
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OUTLINES:
1. What is so “NANO” in microwaves?
SCALES: time, length, energy
2. What do people think of using
microwaves?
Some novel thinking!
3. What I am doing about microwaves
and makes them kind of “nano”!!
Remember I am in the middle of
Taiwan and between no where!
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About Microwaves:
Frequency: about 1GHz~40GHz
Sources up to about 1000 GHz are easily available!
---so called millimeter (submillimeter) wave!
FROM ELVA-1, RUSSIA
http://www.elva-1.spb.ru/
Wavelength:
NOTHING NANO????
(in vacuum)
3m
30cm
100MHz
3
1GHz
3cm
3mm
10GHz
100GHz
300mm
1000GHz
140.120.11.120
E  h
Energy:
(in vacuum)
3m
30cm
E
E/kB
100MHz
1GHz
4×10-7eV
4×10-6eV
5mK
(4.8)
50mK
3cm
3mm
10GHz
100GHz
1000GHz
0.04meV
0.4meV
4meV
5K
50K
0.5K
300mm
Something I can never remember:
h=6.63×10-34J·s =4.136×10-15eV·s
kB =1.38×10-23J·K-1 =8.617×10-5eV·K-1
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Comparison Between Energy Scales
Bandgap of semiconductors
about 0.2~3eV
Conduction-band or
about 30~900meV
valence-band discontinuity
Energy of an optical phonon
about 30~50meV
Energy spacing for a electron in
a typical quantum well (QW)
Fermi energy for electrons in a QW
few meV
Ionization energy of shallow
donors or aceptors
Exciton binding energy
4×10-7eV
E
E/kB
5mK
5
4×10-6eV
50mK
1GHz
about 30~100meV
about 10~50meV
about 5~30meV
0.04meV
0.5K
0.4meV
5K
100GHz
4meV
50K
1THz
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Let’s talk about something related to microwaves
E
Free carrier absorption
EF
phonon
photon
k

At low f (compared to 1/tscatter), it is
just joule heating.
  p2 c
 ( ) 
nr c( 2   c2 )
try some numbers:
nf (cm-3)
1022
fp (Hz)
6
0.9×1015
 
2
p
4n f e 2
m 

1018
1014
0.9×1013
0.9×1011
 m
2 
c ~
 Np 
 m 
1
t
Some possibility here for
quantum dots or lowdimensional
systems
10
10
0.9×109
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Besides microwave
radars, satellite
communications,
ovens…,
what else microwaves
can do?
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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
Radio Astronomy
f0=1.42GHz
0.53Å
Electron spin splittings
Slower than your P4!
Very “NANO”!!
(electron spin resonance ESR)
For free electrons f (GHz)=28.0B(tesla)
0
In semiconductors
DE=g*mBB
g=2
depend on host semiconductors
and fields
GaAs 0.44, GaN 1.98, InSb –51, Ge –2.5, Si 1.98
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Cyclotron resonance
eB
c  
m
B
z
fc(GHz)=28.0(m0/m*)B(tesla)
For electrons confined in a two-dimensional interface
1
1 
E  (n  ) c  g m B B
2
2
Landau levels
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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
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Let’s see the scales again!
E
40meV
400meV
f for EM of
the same l
as SAW
1013Hz
1014Hz
30mm
3mm
3m
lSAW
E
E/kB
4eV
40eV
1015Hz
1016Hz
1017Hz
300nm
30nm
3nm
30cm
3cm
3mm
300mm
100MHz
1GHz
10GHz
100GHz
1000GHz
4×10-7eV
4×10-6eV
0.04meV
0.4meV
4meV
5K
50K
5mK
(4.8)
11
50mK
0.5K
400V
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How to generate SAWs?
First you need a piezoelectric substrate.
Electric field
Mechanical strain
You must place an inter-digit (comb-like)
electrode on the surface as a transducer.
OR
One can use optical
or thermal
methods---but less
defined properties
of SAWs.
laser
SAW
heat
SAW
lSAW
12
You need an e-beam writer to get
“NANO”.
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MORE about SAWs
1. 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.
2. A SAW without an associated piezoelectric field is useless for
microelectronics or nanoelectronics. For example, water wave.
3. 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.
4. The SAW is very useful on detecting the material properties of
the length scale lSAW.
5. The SAW can provide a controllable electrostatic-like field in
the scale of lSAW. Of course the distribution is flying.
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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.
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Anything GOOD to use SAW detectors?!
1. No contact!
2. Short wavelength compared to EM signals at the same
frequency.
3. Low energy compared to EM signals at the same
wavelength.
4. We can use SAWs to detect the special length scale in the
sample via the size-resonance of SAWs and the sample.
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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…….
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Microwave spectroscopy of a quantum-dot molecule
T. H. OOSTERKAMP et al
Nature 395, 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 twodimensional electron gas (2DEG) 100 nm below the
surface.
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Measured pumped current through the
strongly coupled double-dot.
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Determination of the complex microwave photoconductance of a single quantum dot
H. Qin, F. Simmel, R. H. Blick, J. P. Kotthaus, W. Wegscheider, and M. Bichler
Phys. Rev. B 63, 035320 (2001)
Bias dependence of the quantum
dot conductance in the vicinity
of a single resonance.
Amplitude |A| of the
photoconductance measurement
obtained with the two-source setup.
Energy level
alignment.
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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.
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Single-electron acoustic charge transport on
shallow-etched channels in a perpendicular
magnetic field
J. Cunningham et al
Physical Review B 62, pp. 1564-1567 (2000)
fSAW=2.716 25 GHz, I=nefSAW
They are trying to make a new electric
current standard.
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Flying potential and flying electrons
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Quantum computation and spintronics
Quantum computation using electrons trapped by surface acoustic waves
C. 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.
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A Flying Qubit
quantum bit
Spin separation!!
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Spin operation!!
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Toward a quantum computer
a SAW quantum-gate network
Controlled-NOT gate
Probably you need to know some quantum
mechanics before going any further!?
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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….
Acoustically Driven
Storage of Light in a
Quantum Well
C. Rocke, S. Zimmermann,
A. Wixforth, J. P. Kotthaus,
G. Böhm, and G. Weimann,
Phys. Rev. Lett. 78, 4099
(1997);
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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 dot
C. Wiele, F. Haake, C. Rocke, and A. Wixforth
PHYSICAL REVIEW A 58, 2680 (1998)
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Quantum-dot laser with periodic pumping
C.Wiele et al
Physical Review A 60, pp. 4986-4995 (1999)
140.120.11.120
What are we doing in NCHU?
1. 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.
2. We are setting up a simple e-beam writer.
3. We are fabricating high-frequency SAW transducers.
4. We are trying to digging small “nano” holes.
5. We are making lots of microwave connection cables.
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Pulsed RF/Microwave PLL and Gated Averaging System
DC-Coupled Frequency
Modulation (FM)
Directional
Couplers
(B)
(b1)
黑色:低頻訊號
橙色:高頻訊號
Integrator
積分器
(I)
(b2)
Double-Balance
Mixer
PLL
Precision
Counter (C)
Why pulsed?
1.
Use low average power
to prevent from heating
2.
Use gated averaging
technique to avoid
direct EM interruption
3.
Avoid the reflection and
multiple reflection
signals
(M)
RF or (A)
Microwave
Generator
(b3)
Pulse
Generator
(P)
Gated
Average
Time
Delay
(J)
Step
Attenuator
Power
Splitter(S)
(s2)
(s1)
High
Speed
Diode
Switch (D)
(H)Power
Detector
Amplifier
(E)
(G)
Intensity Output
StainlessSteal
StainlessSteal
Semirigid Coax
Z (F)
SAW
Emitter
IDT
Semirigid Coax
Sample
Impedance
Match Network
Active LDES
Region
28
What’s different from others:
SAW
Receiver
IDT
(F) Z
Impedance
Match Network
Cryogenic
Environment
We use type II PLL, homebrew sample-&-hold circuits,
and cheap lock-in amplifiers.
140.120.11.120
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
Power splitter
A home-made
vector meter??
29
To amplitude
detection
Signal from the sample
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Signal Gating & Averaging:
~200 ms set by lock-in amp
s1(t)
Peak power about –30dBm
RF/Microwave pulse train
3~4 ms set by lock-in amp
0.2~2 ms set by pulse
shaping circuit
s1(t)
time delay
Direct coupled EM
s2(t) signal of mixer or power detector
s4(t) signal after SH
Reflected signals
sampling delay set by pulse generator
s3(t)
fed into lock-in
sampling gate set by a pulse generator
fed into the controlling node of a sample-and-hold circuit
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Our system is working------
31
Guess which one is the PLL system?
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A semiconductor chip attached on the SAW delay line
Chip tied on
the SAW
delay line
BeCu SR
coax
5mm
He3 sample
holder
32
IDT SAW
transducer
140.120.11.120
Detection by Phase Lock Loop (PLL)
PLL
system
phase=f1=b1l1
f0 =f1+ fs
fs=bsls =b1l1+bs(B)ls
sample
Sample under detection
Type-II PLL
33
Df0 =0
=Df1+D fs(B)
=Db1l1+Dbs(B)ls
known
B:the parameter
(magnetic field) changed
in the experiment
u:velocity of the wave
D can be measured very
accurately.
140.120.11.120
Reference
From sample
Keep at a constant
phase difference
Reference
From sample
Reference
Df
Due to the change of
sample conditions
Tuning the frequency
to match the phase
From sample
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SAW Delay-Line Sensor
L
l
Du
Df l
1

 
u0
f0 L
2 1  ( xx ／σ
2
K eff
  kSAW
35
2
eff
σ xx /σ M
2 1  (σ xx /σ M ) 2
K
2
)
M


 xx  0 , q    xx  2f 0 ,
2 

l 
 M  u0 (1   2 )
GaAs:3.6×10-7 W-1
GaAs/LiNO3(Y-Z):1.8×10-6 W-1
140.120.11.120
Coplanar Waveguide (CPW) Sensor
 xx 0 , q  0
  xx
G  2
 2D
d eff
 W 1 


 m 
50W meandering CPW
total length ls
Electric
field
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Coplanar Waveguide (CPW) Sensor
Some formulae:
  jm  (  j )  jL(G  jC)
    0   eff
L 1
Z0 


C



2D
xx
 d eff 
37
m  1 m0 m r



  0 eff
 m
2 
 Np 
 m 
ln D
W 
Z0  l
F
 m 
1
C    ,
W
m 
L 
1
m

G
 2 D 1  W1 
   2



d eff   m 
 1     2   rad 
b   m  1  
   

8



   m 

or  2 D  8 2 Df m   L f  d 

xx
 l Z 2 u 

 s 0 L 
2
eff
1/ 2
W 
1
140.120.11.120
Data read from SAW delay line
ns
=2.5×1011
f0=120MHz
T=0.3K
GaAs/AlGaAs
2DES
cm-2
SAW Intensity
Df/f0
0.001%
=1
=2
0
2
4
6
8
10
12
B (Tesla)
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Data read from CPW:
Amplitude (arb. unit)
10
amplitude
8
6
Df
4
200kHz
=2
2
0
=1
f0=1.39GHz
0
2
4
6
8
10
B (T)
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More data:
30
T=0.3K
f0=
2.92G
f0=
25
2.92G
2.16G
20 1.74G
1.74G
1.39G
Df
Amplitude (arb. unit)
2.16G
1.39G
15
0.96G
10
0.96G
0.59G
0.59G
=2
5
0
2
4
6
B (T)
40
500kHz
=1
8
=1
=2
10
0
2
4
B (T)
6
8
10
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High frequency IDT pattern made by
e-beam lithography
Still, not “nano” enough!
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Time delay response of a pulse microwave input
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So-Called
Flows of
MW
modules,
Graduate
students,
………..
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UnderConstruction
^0^
1.
l<1mm
e-beam writer
Nano…..
Nano…..
2. Acoustoelectric effect
V or A
spins
3. Quantum dots, spins, spintronics
Nano…..
Nano…..
Nano…..
Nano…..
Nano…..
Nano…..
Nano…..
Nano…..
4. Buying source of higher
frequency, maybe to THz.
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