Coating processes – Electrical product produced – Resistor for current control
Reexamination Certificate
1999-04-26
2001-10-30
Talbot, Brian K. (Department: 1762)
Coating processes
Electrical product produced
Resistor for current control
C427S125000, C427S126500, C029S610100, C029S620000
Reexamination Certificate
active
06309695
ABSTRACT:
FIELD OF INVENTION
This invention particularly relates to a thick film resistor and a process for the preparation of said thick film resistor useful for making strain gauge with enhanced gauge factor upto 1000.
The thick film resistor of the present invention is obtained by inducing the strain sensitivity in thick film resistor after its fabrication on substrate by coating it with a formulation capable of gauge factor enhancement and subjecting it to high temperature in furnace. The usage of thick film resistor have industrial applications such as hybrid circuit and thermistors etc.
BACKGROUND OF THE INVENTION
The hitherto known strain gauges are of two types. The first one, makes use of metal foil (Micro-Measurements, Measurements Group, Vishay Intertechnology, Inc., P.O.Box 306, 38905 Chase Road, Romulus, Mich. 48174) pressed between two insulating laminates and the second one, uses the silicon material (Kulite Semiconductor International Ltd., One Willow Tree Road, Leonia, N.J. 07605) having diffused layer formed by impurity drive-in at high temperature in an inert gas. The gauges thus formed exhibit 2-5 as the gauge factor for the former type and 45-175 for the latter version. Such gauges are fragile and are temperature sensitive too. The substrate is commonly used to mount the gauge onto it.
There is a definite need for the enhancement of gauge factor for improving the signal conditioners and for developing the sensors for medical applications.
Our studies have shown that such strain gauge of high gauge factor is not available and is not possible with existing material technology. Our studies have also provided us the experimental fact that it is possible to increase the gauge factor by enhancing the conductive phase size of thick film resistive material. As per our process the surface morphology of the thick film resistor material gets converted to long conductive phases and their tunnel distance get enhanced. This in turn decreases the effective sheet resistance and enhances the gauge factor through geometrical and piezoresistive effects. To the best of our knowledge till date such gauges based on thick film technology having enhanced gauge factor are not available internationally.
OBJECTS OF THE INVENTION
The main object of the present invention is to provide a thick film resistor and a process for the preparation of said thick film resistor useful for making strain gauge with enhanced gauge factor upto 1000 overcoming the drawbacks of the hitherto known strain gauges.
SUMMARY OF THE INVENTION
Our invention is based on the experimental fact that it is possible to increase the gauge factor by enhancing the conductive phase size of thick film resistive material. In our process, the surface morphology of thick film resistor material gets converted to long conductive phases and their tunnel distance get enhanced. This in turn decreases the effective sheet resistance and enhances the gauge factor through geometrical and piezoresistive effects.
This also follows from the well known equation for the gauge factor:
Gauge factor=GF
1
∂R/R∂s
=1∂
r/r∂s
+2−1
∂v/v∂s
where R is the resistance, s the strain, r the resistivity v is the volume. Naturally if 1∂r/1∂s is very high, the GF increases very much.
REFERENCES:
patent: 3876560 (1975-04-01), Kuo et al.
patent: 4796356 (1989-01-01), Ozaki
patent: 5206624 (1993-04-01), Patel et al.
patent: 136213 (1991-06-01), None
Council of Scientific & Industrial Research of Rafi Marg
Dickinson Wright PLLC
Talbot Brian K.
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