Page 233 - An Introduction to Microelectromechanical Systems Engineering

212 MEM Structures and Systems in RF Applications

Top electrode
Thin dielectric
Bottom electrode
Isolation
Substrate

(a) (b)
Figure 7.16 Illustration of a membrane switch: (a) In the open state, the metal lines act as a
waveguide, with the sides being ground and the signal propagating down the center line. (b) In
the closed state, application of a dc voltage pulls the top ground membrane down to short the
signal line. If there is a thin dielectric as shown, the impedance is low only at high frequency.
(After: [30].)

Polysilicon
Cap wafer cantilever
Thin gold alloy
Thick gold Motion
Glass Gold/glass
stack forms
Thin gold alloy
hermetic seal
Silicon nitride
Base wafer
Cantilever Ground Signal Ground
drive electrode
Three gold lines form coplanar waveguide
(a)
Polysilicon cantilever
Gold alloy
Silicon nitride insulator Motion signal line
Gold alloy contact
Signal in Signal out

(b)
Thin gold Polysilicon Gold alloy Cantilever 2 Thick gold/glass Contact Input 2 Output
for seal ring cantilever 1 contact 1 drive electrode for seal ring area

Polysilicon Gold alloy Cantilever 1 Input 1
cantilever 2 contact 2 drive electrode
(c) (d)
Figure 7.17 Illustration of the MicroAssembly cantilever switch: (a) Cross section along the
length of the cantilever, showing the coplanar waveguide. (b) Cross section across the width of
the cantilever, showing the signal contact region. (c) Micrograph of the top wafer of a single-pole,
double-throw switch, containing the cantilever, before assembly. (d) Scanning electron micro-
graph of the bottom wafer, containing the coplanar waveguide and seal ring, before assembly.
(Courtesy of: MicroAssembly Technologies of Richmond, California.)