We have developed within a European project a single chip three axis
acceleration sensor. The basic idea is to use independent mechanical
elements for each direction. In case of the accelerations in chip plane
(x,y-direction) comb type structures similiar to tha AD approach has been
used, for accelerations perpendicular to the chip surface (z-direction) a
pendulum type structure has been chosen. The sensors are built up as
differential capacitors and can be used either in open and in closed loop
configuration.  The measured specifications are given in your questionary
below. The targeted application area was the automotive field, therefor we
do not intend to realise a sub g accel. But with that technology a
measurement range of 1g with at least mg resolution is possible.
The technology we have developed for this purpose is the so-called thick
epi-polysilicon surface micromachining. This technology enables the
fabrication of capacitors with basic capacitances in the range of pF, which
allows at least for medium range specs the use of a two chip solution with
mechanical elements and electronics on different chips.

The sensor and the technology has been presented in detail in the following
publications:

B. Wenk, J. Ramos-Martos, M. Fehrenbach, P. Lange, M. Offenberg, W.
Riethmüller
Surface Micromachined Accelerometer with Increased Working Capacitance and
Force Feedback Operation, Proc. ESSDERC`95, The Hague, 25-27 Sept., p.
343-346

M. Kirsten, B. Wenk, F. Ericson, J.A. Schweitz, W. Riethmüller, P. Lange
Deposition of thick doped polysilicon films with low stress in  an epitaxial
reactor for surface micromachining applications Thin Solid Films 259 (1995),
181-187

P. Lange, M. Kirsten, W. Riethmüller, B. Wenk, G. Zwicker, J.R. Morante, F.
Ericson, J.-A. Schweitz
Thick Polycristalline Silicon For Surface Micromechanical Applications:
Deposition, Structuring And Mechanical Characterization Proc. Transducer 95,
Stockholm 1995, 202-205

B. Wenk, J. Ramos-Martos, M. Fehrenbach, P. Lange, M. Offenberg, W.
Riethmüller
Thick polysilicon-based surface micromachined capacitive accelerometer with
force feedback operation Proc. SPIE´95, Vol.2642, Austin/Texas, 23-24 Okt.,
p. 84-94

B. Wenk, W. Riethmüller
A Capacitive Acclerometer as an Example for Surface Micromachined Inertial
Sensors
Proceedings Symposium Gyro Technology 1997, 5.0-5.11, Stuttgart, 16.-17.9.97

If you are interested I can send you paper copies with fax or normal mail.
I

> 1. Researcher or company (references)
>
> Fraunhofer-Institute for Silicontechnology
         Microsystems Department
        Fraunhofer Str.1
        D-25524 Itzehoe, Germany
>
> 2. Noise floor (?mg/root(Hz) or ?micro-g/root(Hz)) (How about
> low frequency?)
>
         equivalent input noise acceleration 0.7m/s2   for  2kHz

> 3. Bandwidth (?Hz) (both sensor measurement bandwidth and resonant
> frequency of proof mass)
        x,y-sensor: 3dB bandwidth 2kHz open loop, 9kHz closed loop
        mechanical resonance frequency of proof mass around 6kHz

        z-sensor: 3dB bandwidth 40Hz open loop, 200Hz closed loop
        mechanical resonance frequency around 2kHz

> 4. Sensitivity (V/g)
>
        x,y sensor: open loop:  16 mV/g, closed loop: 8 mV/g
        z-sensor: open loop: 9 mV/g, closed loop: 6 mV/g
> 5. Dynamic Range (?dB and ?g max)
        up to 100 g

> 6. Working principle (capacitive, tunneling, piezo....)
>
        differential capacitor

         7. Fabrication (Bulk-micromachined, surface-micro...)
        epi-polysilicon surface micromachining

> 8. Proofmass (? milli-gram or ? micro-gram)
        around1.5 ug


> 9. Device area (area including proofmass and cantilever beams or
> membrane:?mmx?mm)
        single axis mechanical element less than 1*1 mm2

> 10. Operating Voltage (high voltage supply :V)
        5V
> 11. Open-Loop or closed-loop with feedback control circuit needed?
        both possible, if closed loop configuration needed depends on
measurement range and related requirements regarding linearity and
bandwidth.

        For the realised x,y- sensor (measurement range 100g, rsolution
0,1g) the closed loop configuration is not necessary. In case of the
z-sensor the closed loop configuration results in a higher bandwidth because
damping effects are reduced. If a mounting under reduced pressure is
possible, the bandwidth will increase and the closec loop may not be
necessary.

> 12. One axis, two axes, or three axes for each sensor unit?
        The three mechanical elements can be fabricated on one chip
        The approach of different elements allows the optimization of the
sensor design with regard to measurement range and sensitivity  for each
axis independently.



        Best regards


Beatrice Wenk

**************************************************************
Fraunhofer-Institut für Siliziumtechnologie
Abt. Mikrosystemtechnik

Fraunhoferstr.1
D-25524 Itzehoe

phone: ++49-4821-17 4508
fax:      ++49-4821-17 4251
e-mail:mailto:[email protected]
homepage: http://www.isit.fhg.de