Platinum resistor for the measurement of temperatures

A platinum resistor for the measurement of temperatures having a silicon substrate, an aluminum oxide film formed on said silicon substrate, and a platinum film formed on said aluminum oxide film.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a platinum resistor for the measurement of 
temperatures, which functions as a temperature sensor. 
2. Description of the Prior Art 
Platinum is chemically stable and can be readily obtained with a high 
degree of purity. Moreover, the electrical resistance of platinum is 
greatly dependent upon temperatures. Thus, platinum has long been used as 
a material for temperature sensors, which is composed of an extremely thin 
platinum wire spirally wound around a mica insulator and a protective tube 
containing the said thin platinum wire therein. These temperature sensors 
are widely used as a resistor for the measurement of temperatures, the 
detailed specifications of which are given in Japanese Industrial Standard 
(JIS) C-1604, DIN 43760 and IEC Pub 751. This resistor for the measurement 
of temperatures is extremely accurate, but it contains such defects that: 
(1) the mechanical strength is poor, 
(2) the production is time-consuming, 
(3) the product is large, and 
(4) the product is expensive. 
In order to eliminate these defects, resistors for the measurement of 
temperature using platinum in a thick or thin layer have been developed in 
recent years, and some are commercially available. However, the resistors 
for the measurement of temperatures including thick platinum layers are 
produced by a screen printing technique, causing problems in that the 
formation of a fine pattern of 100 .mu.m or less is difficult and that 
quality control during production is difficult to maintain. 
On the other hand, the resistors for the measurement of temperatures 
including thin platinum layers have such advantages that: 
(1) a fine pattern is readily achieved, which makes possible 
miniaturization and high resistibility, so that an increase in sensitivity 
of the devices can be attained, 
(2) the mechanical strength is great, and 
(3) as these devices are produced in a wafer, quality control during 
production can be maintained and mass production becomes possible, so that 
the production cost can be reduced. 
The production process for resistors for the measurement of temperatures 
made using thin platinum layers is as follows: A thin platinum layer 
having a thickness of several thousands of angstroms is, first, attached 
to an insulating substrate by a vacuum evaporation method, sputtering, 
etc. The thin platinum layer is then finely patterned by a wet etching 
technique, a sputter etching technique, etc., followed by heating at a 
temperature of 800.degree.-1400.degree. C. in air. Then, trimming is 
carried out to adjust resistance, and the resulting product is cut into 
chips, to each of which lead wires are then connected, resulting in a 
resistor for the measurement of temperatures including a thin platinum 
layer. The insulating substrate is, for example, alumina, sapphire, 
silicon, or glass, each of which has the following advantages and 
drawbacks: 
An alumina substrate is inexpensive and is excellent in the thermal 
resistance, and moreover has an excellent adhesion to platinum, but it is 
inferior in that problems arise with the formation of fine patterns due to 
the roughness of the surface thereof. If the surface is polished, it 
becomes smooth. However, polishing of an alumina substrate, which is hard, 
greatly raises the cost of the substrate. A sapphire substrate is 
excellent in thermal resistance, the adhesion to platinum and the 
smoothness of the surface, but it is inferior in that this substrate is 
most expensive and the operation of cutting it into minute chips is 
difficult. A silicon substrate is relatively inexpensive and smoothness of 
the surface thereof is excellent, and it is easy to be processed. However, 
when it is heat-treated, an alloy of the silicon and the platinum is 
formed, which affects the sensor characteristics thereof. A glass 
substrate is inexpensive, but presents problems such as having a poor 
adhesion to platinum and having no thermal resistance. Thus, all four of 
these substrates have disadvantages as well as advantages, and there is 
still a need for a better substrate. 
SUMMARY OF THE INVENTION 
The platinum resistor for the measurement of temperatures of this invention 
which overcomes the above-discussed and numerous other disadvantages and 
deficiencies of the prior art, comprises a silicon substrate, an aluminum 
oxide film formed on said silicon substrate, and a platinum film formed on 
said aluminum oxide film. 
The aluminum oxide film is, in a preferred embodiment, formed on said 
silicon substrate by a vacuum evaporation method, sputtering, ion-plating, 
chemical vapor deposition, or an anodic oxidation method. 
Thus, the invention described herein makes possible the objects of (1) 
providing a platinum resistor for the measurement of temperatures which is 
inexpensive since a silicon substrate is used; (2) providing a platinum 
resistor for the measurement of temperatures which is excellent in thermal 
resistance since it is made using a silicon substrate and an aluminum 
oxide film; (3) providing a platinum resistor for the measurement of 
temperatures which has a platinum film on an aluminum oxide film covering 
a silicon substrate therewith, so that the formation of an alloy of the 
platinum and the silicon can be avoided and also the adhesion of the 
silicon substrate to the platinum can be excellent; (4) providing a 
platinum resistor for the measurement of temperatures in which a platinum 
film is formed on a silicon substrate with a smooth surface through an 
aluminum oxide film and the surface of the platinum film becomes smooth, 
so that a fine pattern can be formed on the platinum film; and (5) 
providing a platinum resistor for the measurement of temperatures in which 
the substrate is made of silicon so that it is readily cut into chips.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The platinum resistor for the measurement of temperatures of this invention 
is characterized in that an aluminum oxide film is formed on a silicon 
substrate, and a platinum film is formed on the said aluminum oxide film. 
This invention was completed based on knowledge of the inventors that (1) 
either an alumina substrate or a sapphire substrate is excellent in the 
adhesion to a thin platinum film and an alloy is not formed therebetween; 
(2) a silicon substrate is relatively inexpensive, excellent in smoothness 
and moreover easy to be processed; (3) any of the above-mentioned 
substrates has a sufficient thermal-resistance; and (4) thus, by the 
adhesion of an aluminum oxide film to a silicon substrate, the 
above-mentioned disadvantages and the deficiencies of the prior art will 
be able to be solved. 
The platinum resistor for the measurement of temperatures of this invention 
includes not only a thin platinum film but also a thick platinum film. The 
method for the formation of an aluminum oxide film on a silicon substrate 
is, for example, a vacuum evaporation method, sputtering, ion-plating, 
chemical vapor deposition, an anodic oxidation method, etc. In order to 
minimize contamination by impurities, a vacuum evaporation method, 
sputtering or ion-plating is preferably used. 
EXAMPLE 
FIG. 1 shows a platinum resistor for the measurement of temperatures of 
this invention, which comprises a silicon substrate 1, an aluminum oxide 
film 2 formed on the silicon substrate 1, a platinum film 3 with a pattern 
formed on the aluminum oxide film 2, and lead wires 5 connected to the 
platinum film 3. 
This platinum resistor is produced as follows: On the silicon substrate 1, 
the aluminum oxide film 2 having a thickness of several thousands of 
angstroms to several microns is formed by sputtering or ion-plating, 
followed by the adhesion of the platinum film 3 having a thickness of 
several thousands of angstroms to several microns by sputtering or the 
like (FIG. 2). Then, a photoresist pattern 4 is formed on the platinum 
film 3 (FIG. 3), which is then patterned according to the pattern of the 
photoresist 4 by a sputter-etching technique (FIG. 4). The photoresist 4 
is then removed. The product is heated at a high temperature of around 
1000.degree. C. in air and trimmed to adjust resistance. The lead wires 5 
are finally connected to the platinum film 3 by welding, resulting in a 
platinum resistor for the measurement of temperatures. 
It is understood that various other modifications will be apparent to and 
can be readily made by those skilled in the art without departing from the 
scope and spirit of this invention. Accordingly, it is not intended that 
the scope of the claims appended hereto be limited to the description as 
set forth herein, but rather that the claims be construed as encompassing 
all the features of patentable novelty which reside in the present 
invention, including all features which would be treated as equivalents 
thereof by those skilled in the art to which this invention pertains.