Microelectromechanical switch with fixed metal...

Details Microelectromechanical switch with fixed metal... Microelectromechanical switch with fixed metal...

2000-08-24

2002-04-23

Scott, J. R. (Department: 2832)

Electricity: circuit makers and breakers

Electrostrictive or electrostatic

C029S622000, C200S600000, C333S262000

Reexamination Certificate

active

06376787

ABSTRACT:

TECHNICAL FIELD
This invention relates generally to integrated circuits, and more particularly to Micro Electro-Mechanical System (MEMS) switches.
BACKGROUND OF THE INVENTION
Rapid advances in the field of telecommunications have been paced by improvements in the electronic devices and systems which make the transfer of information possible. Switches that allow the routing of electronic signals are important components in any communication system. Switches that perform well at high frequencies are particularly valuable. Although the p-i-n diode is a popular RF switch, it has problems with high power consumption because the diode must be forward biased to provide carriers for the low impedance state. Furthermore, the p-i-n diode suffers from high cost and nonlinearity.
Recently, (MEMS) switches have been developed for switching RF signals.
FIG. 1
shows a cross-sectional view of an RF drumhead capacitive MEMS switch
10
, disclosed by Goldsmith et al. in U.S. Pat. No. 5,619,061. An insulator
14
such as SiO
2
is deposited over a substrate
12
such as silicon. A bottom electrode
16
is formed on insulator
14
and a dielectric
18
is formed over bottom electrode
16
. Capacitor dielectric
18
typically comprises Si
3
N
4
, Ta
2
O
5
or other suitable dielectric materials, for example. An active element comprising a thin metallic membrane
22
is suspended away from electrode
16
by insulating spacers
20
. Membrane
22
is movable through the application of a DC electrostatic field across membrane
22
, which serves as a top electrode, and bottom electrode
16
. Membrane
22
, dielectric
18
and bottom electrode
16
comprise a metal-dielectric-metal capacitor when the MEMS switch
10
is in the “on” position. MEMS switches
10
have low insertion loss, good isolation, high power handling, and very low switching and static power requirements.
SUMMARY OF THE INVENTION
The present invention achieves technical advantages as a MEMS switch having a protective cap formed on the bottom electrode to prevent oxidation of the bottom electrode material, improving the capacitive effects of the MEMS switch. The protective cap comprises a material having a higher resistance to oxidation than the bottom electrode material or a material having an associated oxide, which oxide is a high dielectric contant (k) dielectric material (e.g. at least 20).
Disclosed is a MEMS switch, including a bottom electrode formed over a substrate, and a thin protective cap layer disposed over the bottom electrode. A dielectric material is disposed over the protective cap layer, and a spacer is placed proximate the bottom electrode. A pull-down electrode is disposed over the spacer and the dielectric material. The protective cap layer prevents the oxidation of the bottom electrode.
Also disclosed is a method of manufacturing a MEMS switch, comprising the steps of providing a substrate, depositing an insulator layer on the substrate, and forming a bottom electrode on the insulator layer. A thin protective cap layer is deposited over the bottom electrode, and a dielectric material is deposited over the bottom electrode and thin protective cap layer. A pull-down electrode is formed over the dielectric material. The thin protective cap layer prevents the oxidation of the bottom electrode.
Advantages of the invention include maintaining the capacitance of the dielectric stack of a MEMS switch. The protective cap layer comprises a material having a higher resistance to oxidation than the bottom electrode or a material that forms a high dielectric constant oxide upon oxidation, maintaining or improving the capacitance to the dielectric stack. The protective cap layer is easily implemented and only requires one more processing step.


REFERENCES:
patent: 5619061 (1997-04-01), Goldsmith et al.
patent: 5638946 (1997-06-01), Zavracky
patent: 6100477 (2000-08-01), Randall

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