JPH02167462A - Light shielding type chemical sensitive element - Google Patents

Abstract

PURPOSE:To eliminate the adverse influence on light and to maintain a good temp. characteristic by forming an SiO2 film between at least a metallic film for light shielding and ion sensitive film of this element. CONSTITUTION:A Cr film 4 is deposited by evaporation on a protective film 3 of a PH-ISFET (hydrogen ion sensitive field effect transistor) 11 in order to provide light shielding on this film and the entire area of the periphery (hatched part) of a gate part 12 including a gate part 12. The SiO2 film 5 is then laminated thereon to cover the metallic film 4. A Ta2O3 film is further laminated as a sensitive film 6 on the SiO2 film 5 from above so as to cover this film. An insulating film 2 and the protective film 3 are thus formed on a substrate 1 consisting of P-Si which is crystalline Si and the metallic film 4, the SiO2 film 5 and the sensitive film 6 are formed thereon. The SiO2 film 5 is selected because this film has a good adhesive property and the SiO2 is used for the insulating film 2. The exact measurement in a b right place is possible in this way and the element is usable for the measurement in the state of the good temp. characteristic.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a chemically sensitive element for detecting the ionic activity in an electrolytic solution and the concentration of the electrolytic solution.

[Prior art] In recent years, attempts have been made to create sensors for various ions, enzymes, gases, humidity, etc. using field effect transistors, and Professor Matsuo and others at Tohoku University have conducted pioneering research. 9 The above-mentioned sensor is manufactured based on a hydrogen ion photosensitive field effect FET in which the metal terminal of the gate portion of the field effect transistor is removed.

For example, in the case of a K ion-sensitive l5FET,
Hydrogen ion sensitive membrane (Ta2) of TSFET
0. , Si, N4, etc.) by forming a vinyl chloride resin film containing a halinomycin plasticizer.

However, since the 15FET is made of a semiconductor, it is fundamentally affected by light and temperature, so even after it was manufactured as a sensor, it was necessary to take temperature and external light into account when making measurements.9 For this reason, the applicant As shown in Japanese Unexamined Patent Publication No. 59-102154, it has been proposed to eliminate the influence of light by shielding the PH-ISFET with a metal film.

As shown in FIGS. 10 and 11, l formed of semiconductor
5FET], ], a gate part 12 which is an ion sensing part of
Lead portions 13 and 14 of the source S and drain D are provided respectively, and a protection M is provided to shield the entire semiconductor surface from light.
A metal film 4 is formed on 3.

Note that 2 is an insulating film provided on the substrate 1, and 5 is a sensitive film.

[Problem to be solved by the invention] In order to remove the influence of light and improve the controllability of temperature characteristics, further research was conducted on the '42 IspET using a metal light shielding film, and it was found that the 15FET with a metal light shielding film was It was found that the temperature characteristics deteriorated extremely.

In the case of a PI-(-ISFET) without a metal light-shielding film, the temperature characteristics are approximately +2,8 as shown in Figure 12A.
mv/°C, and the reproducibility with respect to temperature rises and falls was also good.9 On the other hand, the temperature characteristics of the 15FET with a metal light-shielding film fluctuated greatly, as shown by the dotted line in Figure B. Reproducibility was also poor9 However, the source. When measurements were performed while changing the drain current Id, the temperature characteristic value showed a tendency to decrease as the current increased both in the case without the light shielding film and in the case with the light shielding film.

Further, when a Riet wire is drawn out from one end of the light-shielding film and the device is operated as an MO8 type FET, the temperature characteristics exhibit the same temperature characteristics as when there is no light-shielding film. From the above, it is thought that the cause of this deterioration in temperature characteristics is a problem with the adhesiveness of the sensitive film.

An object of the present invention is to provide a light-shielding chemical sensitive element which is provided with a metal light-shielding film and which eliminates the adverse effects of light and also has good temperature characteristics.

[Means and effects for solving the problem] This light-shielding chemically sensitive element enables accurate measurement in bright places by forming at least 5iC)+M between the light-shielding metal film and the ion-sensitive film. In addition, it can be used for measurements with good temperature characteristics.

[Example]] As shown in FIGS. 1 and 2, a hydrogen ion sensitive field effect transistor (PH-ISF) was manufactured by a conventional method.
On the protective film 3 of the ET) 11, a Cr film 4 is deposited to a thickness of about 180 OA in order to shield the entire peripheral surface of the gate part including the gate part]2 (the shaded area).

Next, insulating S]0 was applied by sputtering to cover the Cr[4].
Two films 5 are laminated to a thickness of about 2000 OA.

From this 5102 film 5, approximately 1 203 film is further coated as a sensitive film 6 by sputtering so as to cover it.
oooX stack.

An explanatory cross-sectional view of the gate part 12 laminated in this way is shown in FIG. metal! A 4.5in2 film 5 and a sensitive film 6 are formed.

The 5in2 film to be deposited on the metal film 5 was selected because of its good adhesion and because SjO was used for the insulating film 2.

When measurements were taken using the light-shielded hydrogen ion-sensitive field effect transistor formed in this way, it was not affected by light, and its temperature characteristics were extremely stable as shown in Figure 3A. Also table [2 as shown in 1F
, 0 mv/°C.

Incidentally, FIG. 3P shows the temperature characteristics of an 15FET without a light shielding film.

In order to wrap the metal film with 5102M, SiO2 films were formed on the top and bottom of the metal film. The second 5102M7 is approximately 100O
9. On top of that, Cr is removed to a thickness of
114 to a thickness of 180 OA, and then a Si○2 film 5
, Ta2O, and the film 6 are laminated to a thickness of about 1000 nm by sputtering.

By forming in this way, the protective film (Si2N4) 3
Since there is no direct contact between the metal PLA 4 and the metal PLA 4, the adhesion between each film is further improved, and stable operation 4 can be achieved over a long period of time. In addition, the temperature at this time [Example 3] As shown in FIG. 5, this example shows the source S and train D portions of the 15FET made by the usual method, and the elongated source from the train terminal 13 portion as shown by diagonal lines. - A metal film 4 is provided over the train pull-out portion.

That is, Cr is deposited to a thickness of 1800 Å on the upper surface of the protective film 3 to form the light-shielding metal film 4. On top of that, SiO2 film 5
is laminated to a thickness of 200 OA by sputtering, and then Ta205 JIK6 is further laminated to a thickness of 1000 OA by sputtering.
Although the PN junction of the elongated source/drain lead-out portion is covered from the train D portion, the entire portion may be covered. Further, either the source or the train may cover both at the PN junction of the source/drain lead-out portion.

Since the photoresponsiveness of the 15FET formed in this way exhibits the properties of a photodiode (the photoresponsivity does not change even if the VS2 is changed), the PN junction in the reverse bias state, that is, the vicinity of the drain, is shielded from light. Not only is this effective, but also the stability can be increased by forming the edge part in this way, since stress tends to occur in the edge part, which tends to affect the temperature characteristics.

The temperature characteristics at this time showed extremely good characteristics as shown in Figure 3C, and the value was 2.3mV as shown in Table [1F].
/°C, which was good.

[Example 4] This example is based on the metal film 4 of the third example as shown in FIG.
A second SiO□ film 7 is also provided on the lower side of the second embodiment, which is similar to the second embodiment.

Note that the thickness of each 5in2 film in this case is 1000A.

The following table [+1 is PH-rsFE in each of the above embodiments]
This shows the temperature characteristic value of T, and the experimental conditions were V2C-]V
, Id=50μA.

The smaller the error in the temperature characteristic value at this time, the better the correlation between the temperature and the 15FET output, and the more accurate temperature compensation can be performed.

[Example 5] In this example, as shown in FIG.
Two films 5 are formed. That is, as in the first embodiment, the 5102 film 5 is first formed to a thickness of about 30 OA on the surface including the gate portion of the pl-1-ISFET by sputtering. Second, as in the first embodiment, C1-
The film was deposited to a thickness of 1880 OA, and the film was spudged with Ta2O as the sensitive M6 at 56 ± 03 m/°.
Although it showed a relatively large temperature gradient compared to C, the reproducibility was also good.

Table [■] <Film thickness unit is A. P■] Responsiveness of the PH-1sFETs formed in each example as shown in 2 below, an output of 55 mv/PH has been obtained in all cases. Furthermore, as shown in FIG. 9, Examples 1 and 2, in which the entire surface was covered with a metal light-shielding film, had light-shielding properties (
As shown in (b), the property without coating (g)]0 was about 1725, and in Examples 3 and 4, the property was also reduced to about 174, as shown in property (d).

The characteristics shown in FIG. 9 are those in which the thickness of the metal light-shielding film is 1200 mm.

Note that the present invention is not limited to the embodiments described above, and the substrate of the 15FET (2 crystals S1 was used, but the n-
8i crystal or amorphous Si or P-Si.

n-3i and 5O5 (Si con on 5apphi
re) structure, 5OI (Silicon On In5u)
latOn) structure, etc. In addition, the ion-sensitive membranes are also 5I3N, Pl;O□, IrO2, other than Ta2O,
RIIO,...○s, Ti○2 may also be used.

The film thickness at this time is preferably in the range of 500 to 300 OA,
And the coating is on the entire surface except for the terminal part of the source train.
You can also add it.

Furthermore, the 5jO7 film and the Ta204 sensitive film can also be laminated by vapor deposition, CVD, etc., and the M thickness of each film is 1.
A range of 00 to 5000 A is desirable.

[Effects of the Invention] According to the present invention, it is possible to provide a light-shielding scientific element that has good temperature characteristics even when coated with a light-shielding film and has good reproducibility without impairing the function of PII=ISF[T.

[Brief explanation of the drawing]

FIG. 1 is a light-shielding scientific sensing element for explaining one embodiment of the present invention, FIG. 2 is an enlarged explanatory cross-sectional view taken along line AA in FIG. 1, and FIG. 3 is an illustration of each embodiment of the present invention. FIG. 11 is a diagram for explaining a conventional scientific sensing element, and FIG. 12 shows temperature characteristics related to the presence or absence of light shielding. 4.Metal light-shielding film 5.5102 6-.Sensitive film 11-.l5FET Nostalgia- Figure 6/12 (mv) Figure 8

Claims (4)

[Claims] (1) A metal film such as Cr, Al, Ta, Ag, etc. is coated as a light-shielding film on the ion-sensitive field effect transistor, and Si_3N_4, Ta_2O_5 is used as the ion-sensitive film.
, PtOx, JrO_2, RUO_2, OSO_2, T
A light-shielding chemical sensitive element formed by laminating iO_2 or the like, characterized in that an SiO_2 film is formed on either or both of the upper and lower surfaces of the light-shielding film. (2) The light-shielding chemical sensitive element according to claim 1, wherein the SiO_2 film has a thickness of 100 to 5000 Å. (3) A claim characterized in that the metal film is such that one of the source and the drain covers both at least the source/drain portion and the PN junction of the source and drain extraction portions of the ion-sensitive field effect transistor. Item 1. The light-shielding chemically sensitive element according to item 1. (4) The light-shielding chemically sensitive element according to claim 1, wherein the metal film covers the entire surface of the ion-sensitive field effect transistor.