mems variable inductor for multi-band rf cmos …masu- variable inductor ... mems actuator is used...
TRANSCRIPT
Hirotaka Sugawara, Yoshiaki Yoshihara, Hiroyuki Ito, Kenichi Okada, and Kazuya MasuPrecision and Intelligence Laboratory, Tokyo Institute of Technology, Japan
MEMS Variable Inductor for Multi-band RF CMOS Circuits
3. Measurement Results
1. Background
2. Principle of Variable Inductor
On-chip inductorsThe demand has been increasing for RF Si CMOS circuits.
Parallel-plate ActuatorMEMS Actuator
Comb actuator stationary electrode
movable electrode
Parallel-plate actuator
stationary electrode
movable electrode
W. C. Tang, M. G. Lim, and R. T. Howe: J. Microelectromechanical Systems 4 (1992) 170.
V. M. Lubecke, and J. -C. Chiao: The IEEE 4th Int. Conf. on Telecommunications in Modern Satellite, Cable and Broadcasting Services, 1999 p. 1
The actuators are driven by electrostatic force. By generating DC bias between the stationary electrode and the movable electrode.
MEMS actuator is used for moving the metal plate above the spiral inductor
Variable Inductorconsists of a planar-type spiral inductor and a metal plate.Metal Plate
Spiral Inductor
h
x
Moving
The inductance continuously varies depending on the position of the metal plate.
The metal plate shields the magnetic flux whichpenetrate the inductor.
The inductance value can be also varied by changing the height of the metal plate.
Small h ・Variable range of inductance increases.・Parasitic Capacitance increases.
Shielding Magnetic Mechanism
Metal Plate
L [n
H]
0.8
1.8
Relative Permeability µ0.01 1 10000100
1.01.21.41.6
L [n
H]
0.8
1.8
Conductivity σ [S/m]1 102
1.2
106 108104 1010
1.41.6
1.0
L [n
H]
1.8
1.41.6
Thickness of Metal Plate [µm]0.01 0.1 100101
1.21.00.8
x
h
Thickness
Spiral InductorTurns : 2.5Line width W : 20 µm Line space S : 10 µmOuter dimension D : 250 µmL=1.8 nH
Simulated by HFSS (Ansoft)
Metal Thickness of over Skin Depth
Magnetic flux can be shielded by the metal plate
2Depth Skin =
Skin Depth≒2µm @1GHz
2Depth Skin =
Skin Depth≒2µm @1GHz
2Depth Skin =
Skin Depth≒2µm @1GHz
ωσµ
Measurement Method
Effect of Parasitic Capacitance
Input Impedance
Equivalent circuit model
subsub
2sub
metmet
2met )()(ssin
LjωRM
LjRMLjRZ
ω
ωωω
++
+++=
The magnetic fluxpenetrates the metal plate.
Eddy current flows in the metal plate.Eddy current flows in the metal plate.
Induced a counteractive magnetic field according to Lenz’s Law.
Induced a counteractive magnetic field according to Lenz’s Law.
The metal plate shields the magnetic flux.The metal plate shields the magnetic flux.
Inductance change
Change of the magnetic flux
+−
++
++
++=
2sub
2sub
sub2
sub2
met2
met
met2
met
2sub
2sub
sub2
sub2
met2
met
met2
met
)()(
)()(-s
)()(
)()(s
LRLM
LRLMLj
LRRM
LRRMR
ωωω
ωωω
ωω
ωω
PurposeTo realize a variable inductor on Si CMOS chip
( )( )inRe
inImZZQ =
The variation Q is smaller than that of L
The wireless communication system has several frequency bands which are required to cover several frequency bands.
Variable RF InductorWide-range oscillation of VCO
Wide-tunable impedance matching
Multi-band solutions are required to cover several frequency bands.
Multi-band solutions are required to cover several frequency bands.
The metal plate is moved by DC bias between the stationary electrode and the movable electrode
Lower Power Consumption
The variable inductor is an indispensable device for high-frequency and multi-band circuits.
MEMS actuator requires high manufacturing cost, and the reliability is not so high at the present time.
h
Spiral Inductor
Metal Plate
Stationary Electrode
Arm
current does not flow between the electrodes
De-embedding・ Open and short pad are used
openshortopenmeas
ind
111
YYYY
Y
−−
−
=
De-embedding・ Open and short pad are used
openshortopenmeas
ind
111
YYYY
Y
−−
−
=
( )
( )( )de
dm
dm
ZRZIQ
ZI1L
=
=
( )2ind12
ind22
ind11
ind12
ind12
ind11
dYYY2YYYZ
−
++=
ω
DUT
Open pad
Short pad
Frequency [GHz]0.1 1 10
L [n
H]
0
12
8
4
16h=100 µmh=10 µm
Frequency [GHz]0.1 1 10
Q
12
4
0
3
5h=100 µmh=10 µm
Height of plate h [µm]
3.5
L [n
H]
0 20 80
6.5
4.5
5.5
6040 100
f =2.45 GHzx=500 µm
Height of plate h [µm]
2
Q
0 20 80
5
3
4
6040 100
f =2.45 GHzx=500 µm
Variable Range:34.6% Variable Range:26.3%
The parasitic capacitance is induced between the spiral inductor and the metal plate
LCf
21
SR =π
⇒Degrade the inductor characteristics
Height of plate h [µm]
00 20 80
0.10
6040 100
C [p
F]
0.080.06
0.020.04
Height of plate h [µm]
50 20 80
8
6
7
6040 100
fSR [G
Hz]
h decreases⇒fSR decreasesEffect of parasitic capacitance is not dominant
Parasitic capacitance is not increased so much by metal plate
Height of plate h [µm]
500 20 80
100
70
90
6040 100
Im(Z
in)
80
60 f =2.45 GHz
Re(
Zin)
Height of plate h [µm]
200 20 80
30
25
6040 100
35
40
f =2.45 GHz
LS
RS
Lmet
Rmet
Metal PlateSpiral Inductor
Lsub
Msub
RsubZin
Mmet
h decreasesMmet increases⇒Im(Zin) decreases
Msub decreases⇒ Re(Zin) decreases h decreases
Mmet increases⇒Im(Zin) decreases
Msub decreases⇒ Re(Zin) decreases
⇒Variation of Q is small
Appendix. Redistributed Layers
Si
SiO2 Al
CuResin
Cu:10 µmResin:10 µmAl:1.5 µmSiO2 :0.5 µmSi:525 µmSi resistivity A: 2-6 Ωcm B: 1k Ωcm DUT with pad Open pad
Height of plate [µm]0
4
50
3
2150100 200
5
A (ρ=2−6 Ωcm)
B (ρ>1 kΩcm)Variable range:53.1%
Variable range:52.4%
L [n
H]
10
50
20
30
Height of plate [µm]0 50 150100 200
40
0
60
A (ρ=2−6 Ωcm)
B (ρ>1 kΩcm)Variable range:48.8%
Variable range:61.0%
Q
Frequency [GHz]
L [n
H]
2
0
4
0.1 1 10
10
6
8 A (ρ=2−6 Ωcm)B (ρ>1 kΩcm)
Frequency [GHz]0.1 1 10
Q
0
10
50
20
30
40
60A (ρ=2−6 Ωcm)B (ρ>1 kΩcm)
@ f=2 GHz
The variable range of L
53 % in Inductor A 52 % in Inductor BThe variable range of Q
50 % in Inductor A 62 % in Inductor B
WL-CSP wafer-level chip-scale packagesLead free bump
2nd Resin Inductor
Die
1nd ResinCu reroutingAl pad
K. Itoi, M. Sato, H. Abe, H. Sugawara, H. Ito, K. Okada, K. Masu, and T. Ito: IEEE MTT-SInt. Microwave Symp. Digest, Fort Worth, 2004 p. 197.
WL-CSP Advantages・Thick Cu conductor ・Resin layer between the conductor and Si substrate
Reduction in substrate loss ⇒High-Q
WL-CSPThe CMOS chip's pads are connected to the board's pads through lead free bumps and redistributed layers.
Inductance is implemented using redistributed layer
Metal Plate
[without inserting]
[with inserting]