Polycrystalline silicon-germanium films for micro-electromechanical systems application

DETAILED DESCRIPTION The present invention is directed to the use of a Si.
sub.
1-x Ge.
sub.
x, material, where 0<x.
ltoreq.
1, for fabricating MEMS devices.
The present invention will be described in terms of several representative embodiments and process steps in fabricating a MEMS resonator with pre-existing microelectronics.
Poly-SiGe is a semiconductor alloy material which has properties similar to Poly-Si, but can be processed at substantially lower temperatures.
Table 1 provides a comparison of the various properties of poly-Si and poly-Ge.

TABLE 1
Properties of poly-Si and poly-Ge
Poly-Si Poly-Ge
Thermal Properties:
Melting temperature (.
degree.
C.
) 1415 937
T.
sub.
deposition (.
degree.
C.
) -600 -350
T.
sub.
stress anneal (.
degree.
C.
) 900 <550
Thermal expansion (10.
sup.
-6 /K) 2.
6 5.
8
Mechanical Properties:
Young's Modulus (Gpa) 173 132
Fracture strength (Gpa) 2.
6 +/- 0.
3 2.
2 +/- 0.
4
Electrical Properties:
Bandgap at 300 K (eV) 1.
12 .
66
Electron affinity (V) 4.
15 4.
00
FIG.
1A shows the top view of device 120 including a CMOS trans-resistance amplifier 100 and a microresonator 105 in a side-by-side configuration.
The resonator 105 is a comb-drive device fabricated with microfabrication equipment using p-type Si.
sub.
1-x Ge.
sub.
x, where 0<x.
ltoreq.
1, as the structural material and Ge as the sacrificial material.
In this particular device, x=0.
64.
Resonator microstructures are described in U.
S.
Pat.
Nos.
5,025,346; 5,491,604; 5,537,083; and 5,839,062.
These patents are all assigned to the assignee of the present application and are incorporated herein by reference.
The amplifier 100 may include one or more transistors.
The transistors may be MOS or bipolar transistors.
The transistors may be formed on a silicon substrate