Tackya Yammouch, Hirotaka Sugawara, Kenichi Okada, and Kazuya Masu Precision and Intelligence Laboratory, Tokyo Institute of Technology, Japan
A Large Variable Ratio On-Chip Inductor with Spider Legs Shield
Radio Band Spreading Widely
Inductor on Si RF Circuit MEMS 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
MEMS actuator is used for moving the metalplate above the spiral inductor
A chip can supportonly a narrow band.
DTV
WideBand
WLAN
Blue-tooth
RFID The chip possibleto support wideband is necessary.
↓
→ ←
→ ←
vdd
vctrl
Example of Si RF Circuiton-chipinductor Inductance depends
on the shape.
Inductance valuesare constant.
Impossible tosupport wide band.
If inductors can have variableinductance value, Si RFcircuits that support wideband can be realized.
Conventional Variable Inductor
Metal Plate Metal Plate
Metal plate cancels magnetic flux. But...
Some of fluxes cannot be canceled.
Proposed Variable Inductor
Metal Plate Metal Plate
Shield metals cancel the undesired flux.Φmax/Φmin increases. Thus, variableratio increases.
1. Background
2. Proposed Structure of Variable InductorShielding Magnetic Mechanism
The magnetic fluxpenetrates themetal plate.
Eddy current flowsin the metal plate.
Induced a counter-active magneticfield according toLenz's Law.
The metal plateshields themagnetic flux.
Inductance valueis changed.
Change of themagnetic flux
3. Result of SimulationSimulation Method
outer diameter D = 300 µmline width W = 20 µmline space s = 1.2 µmshield width W = 20 ~ 250 µm
height of metal plate h = 10 µm or
Metal Plate
ShieldMetal
Inductor
h
7.65 µm
0.95 µm
Shield metals consist of 5 layers from M5 to M1.The inductor is made in M5.Simulation is performed by HFSS(Ansoft).
Variable Range of Inductance Value
The variablerange @ 5 GHz
The variableratio @ 5 GHz
conventional
proposed(W = 165 µm)
1.03~2.59 nH
0.83~2.37 nH
2.53
2.8714% up
4. ConclusionThe maximum variable ratio of inductance is 2.87 @ 5 GHz・The variable ratio increases 14% @ 5 GHz・
The proposed variable inductor can be applied to Si CMOS RF circuits,and improves the tuning range of circuits.
Variable ratio r is calculated as follows.r = Lmax/Lmin
Φmax = 11
Φmin = 6
Φmax = 7Shield Metal
Φmin = 2
W
wsD
Metal Plate
It is assumed to use 0.18 µm CMOS process.
8
Magnetic Field around the Inductor
Simulated by HFSS(Ansoft).
InductorInductorShield Metal
Magnetic flux isreduced by theshield metal.
0
1
2
3
4
0.1 10 1
No ShieldShieldNo Shield with Metal PlateShield with Metal Plate
(i)(ii)(iii)(iv)
frequency [GHz]
L [n
H]
W = 165 µm
0
1
2
3
4
5
0.1 1 10
No ShieldShieldNo Shield with Metal PlateShield with Metal Plate
(i)(ii)(iii)(iv)
frequency [GHz]
Q
W = 165 µm
2.4
2.6
2.8
3.0
0 50 100 150 200 250
f = 5 GHz
No Shield
Shield width W [µm]
Varia
ble
Rat
io r
14% up
Hi
Lo
6.0 GHz
400 MHz
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