1 Introduction
2 Design of the RF MEMS varactor
Symbol | Description | Value |
---|---|---|
L
| Length of the beam | 550 µm |
g
0
| Air-gap | 3.1 µm |
t
d
| Thickness of dielectric layer | 0.25 µm |
ɛ
r1
| Relative permittivity of dielectric layer | 7.5 |
t
| Thickness of the beam | 2 µm |
w
t
| Width of the truss beam structure | 5 µm |
t
s
| Silicon substrate thickness | 525 µm |
ρ
| Resistivity of silicon substrate | 10 k Ω m |
W
| Width of the co-planar waveguide transmission line | 80 µm |
G
| Gap of the co-planar waveguide transmission line | 50 µm |
A
1
| Area of bit-1 of the varactor | 10 µm × 40 µm |
A
2
| Area of bit-2 of the varactor | 20 µm × 40 µm |
A
3
| Area of bit-3 of the varactor | 40 µm × 40 µm |
A
4
| Area of bit-4 of the varactor | 80 µm × 40 µm |
A
5
| Area of bit-5 of the varactor | 160 µm × 40 µm |
t
SU-8
| Thickness of SU-8 layer | 0, 5, 10,15, 20, 25, 30 µm |
ɛ
r2
| Relative permittivity of SU-8 | 4 |
tan δ
SU-8
| Loss tangent of SU-8 | 0.04 |
A
el
| Area of pull-down electrode | 1.82 × 10−9 µm2
|
E
| Young’s modulus of aluminium | 69 GPa |
V
p
| Pull-down voltage | 30.31 V |
V
h
| Holding voltage | 25 V |
k
T
| Spring constant | 1.33 N/m |
C
d(max)
| Maximum capacitance value | 3.57 pF |
C
u(min)
| Minimum capacitance value | 102.23 fF |
C
r
| Capacitance ratio | 35.7 |
3 Results and discussions
3.1 Electro-magnetic simulations
Thickness (µm) | Capacitance ratio | Q-factor (upstate/downstate) |
---|---|---|
0 | 16.9 | 248/95 |
5 | 24.5 | 505/114 |
10 | 28.9 | 613/108 |
15 | 34.4 | 762/93 |
20 | 34.8 | 812/50 |
25 | 34.6 | 648/66 |
30 | 33.5 | 827/62 |