Micromechanical angular accelerometer with auxiliary linear accelerometer

DETAILED DESCRIPTION OF THE INVENTION Referring to FIGS.
1 and 2, a micromechanical accelerometer 20 comprises a transducer element 22 which is suspended by a pair of flexible linkages 24 above a void 26 in a mass of silicon 28.
The silicon mass 28 is preferably an N-type epitaxialy grown layer on a base of monocrystalline N-type silicon.
Selective doping and etching yields P-type transducer element 22 and flexible linkages 24 freely suspended in a frame 30 above void 26.
Processes for selective doping and etching of silicon mass 28 are described in the above-referenced applications.
Transducer element 22 includes a substantially symmetrical plate 32, torsionally supported by linkages 24, doped P-type and selectively etched free from silicon mass 28.
A plurality of etch facilitating slots 34 are formed through plate 32 to speed up and assure complete undercutting of plate 32 during formation of void 26 and release of element 22 from silicon mass 28.
The pair of flexible linkages 24 have first ends 36 connected to silicon frame 30 and second ends 38 connected to plate 32.
The plate 32 is completely detached from silicon mass 28 and free to rotate about an axis formed by the flexible linkages 24.
If the flexible linkages 24 are created by selectively P-type doping areas defining the linkages 24 and plate 32, the resulting transducer element 22 is effectively isolated from silicon mass 28 by the P-N junction between P-type flexure and N-type mass 28 created by doping the flexure and plate areas.
Alternatively, dielectric isolation of transducer element 22 can be achieved by growing an oxide or silicon nitride layer or combination thereof or the like over the N-type mass 28, as described in the referenced applications, to form flexible linkages thereon.
Dielectric isolation will provide much lower capacitance between the plate 32, flexible linkages 24 and the remainder of mass 28 permitting a device having a significantly greater signal-to-noise ratio than a similar device having P-N junction isolation of plate and flexures