Browse Prior Art Database

Micromechanical Thermogravimetry (MMTG)

IP.com Disclosure Number: IPCOM000123089D
Original Publication Date: 1998-May-01
Included in the Prior Art Database: 2005-Apr-04
Document File: 2 page(s) / 93K

Publishing Venue

IBM

Related People

Berger, R: AUTHOR [+7]

Abstract

There are two types of such commercial TG instruments: One is a deflection-type instrument, where a deviation of a balance beam from its null position is detected. The other is a null-type instrument, which uses a feedback system to apply restoring forces, proportional to the mass change (1).

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Micromechanical Thermogravimetry (MMTG)

   There are two types of such commercial TG instruments: One
is a deflection-type instrument, where a deviation of a balance beam
from its null position is detected.  The other is a null-type
instrument, which uses a feedback system to apply restoring forces,
proportional to the mass change (1).

   Disclosed is a new method for thermal analysis of nanogram
to picogram quantities of material using a MMTG technique.  The key
feature of the microsensor used is its ability to weigh samples and
simultaneously to perform controlled temperature cycles using a
piezoresistive layer integrated into the micromechanical cantilever.
The technique outperforms current thermogravimetric approaches by
five orders of magnitude.  As an example quantitative analysis of the
dehydration of copper-sulfate-pentahydrate '(CuSO' <sub 4> % dot %
'5H' <sub 2> 'O)' is given.  The operational setup of the MMTG
technique is schematically illustrated in Fig. 1(A).  Piezoresistive
cantilevers used for scanning force microscopy (SFM) are able to
detect subangstrom mechanical deflections and are particularly
suited to determine the cantilever's vibrational amplitude.
Resistivity changes of the piezoresistive layer in response to a
stress change when the sensor is deflected is measured using a
Wheatstone bridge (WB).  The applied bridge voltage produces an
electrical power dissipation which heats the micromechanical device
(2).  For detecting only the cantilever deflection, as in SFM the
bridge voltage is kept at a constant value.  In the disclosed new
technique however, the bridge voltage is ramped, which increases the
electrical power, producing a temperature increase of the cantilever.
In addition to heating, the temperature of the micromechanical
cantilever can be determined by measuring the resistivity of the
piezoresistive layer, which permits the sensor to be subjected to
controlled temperature cycles.  The micromechanical cantilever can be
thermally cycled from 300 K to above 800 K and its deflection can be
detected simultaneously from the additional stress-induced change in
piezoresistance.  This enables to measure the cantilever resonance
freque...