SU1509719A1 - Device for measuring concentration of ions in solutions of electrolytes - Google Patents

Abstract

The invention relates to a measurement technique, to the measurement of the concentration of ions in electrolyte solutions and can be used most effectively in analytical systems with a small volume of samples under study. The aim of the invention is to improve measurement accuracy by fully compensating for the temperature sensitivity of the indicator transistor and auxiliary electrode, by reducing the time drift, hysteresis of characteristics and low-frequency noise level by forming a dielectric layer on the sensitive area of the auxiliary transistor without a metal gate electrode 50 mm thick. times the thickness of the dielectric layer of the indicator transistor. In this case, the substrate of the indicator transistor is connected to the common bus of the device, and the output of the operational amplifier is connected to the auxiliary electrode. A device for measuring the concentration of ions in electrolyte solutions contains indicator 1 and auxiliary 2 transistors and auxiliary electrode 3 placed in test solution 4 in vessel 5, first 6 and second 7 voltage sources, current source 8, current reflector 9, operational amplifier 10, temperature compensation unit 11, voltmeter 12. Indicator 1 and auxiliary 2 transistors are located in the semiconductor substrate 13, are covered with a dielectric layer 14, and above the sensitive area 15 of the indicator transistor 1 they form An dielectric layer is from 20 nm to 200 nm, and over the sensitive area 16 of the auxiliary transistor 2 is a dielectric layer of more than 1 micron. Due to the negative feedback loop, the voltage on the drains of the indicator 1 and auxiliary 2 transistors is maintained in the same way by changing the voltage on the auxiliary electrode 3 in such a way that the voltage of the electric field in the dielectric is kept close to zero. The device allows to improve the identity and reproducibility of the characteristics by reducing the time drift and hysteresis and to improve the accuracy of measuring the concentration of ions. 2 Il.

Description

of the auxiliary transistor without a metal gate electrode, whose thickness is 50 times greater than the thickness of the dielectric layer of the indicator transistor. In this case, the substrate of the indicator transistor is connected to the common bus of the device, and the output of the operational amplifier is connected to the auxiliary electrode. The device dp of measuring the concentration of ions in electrolyte solutions contains indicator, 1 and auxiliary 2 transistors and auxiliary electrode 3 placed in test solution 4 in vessel 5, the first 6 and second 7 voltage sources, current source 8, current reflector 9 , operational amplifier 10, temperature compensation unit 1, volt-meter 12. Indicator 1 and auxiliary 2 transistors are located in

the semiconductor substrate 13 is covered with a dielectric layer 14, a dielectric layer of 20 to 200 nm is formed over the sensitive area 15 of the indicator transistor 1, and a dielectric layer of more than 1 μm is above the sensitive area 16 of the auxiliary transistor. Due to the negative feedback loop, the voltage on the drains of the indicator 1 and auxiliary 2 transistors is maintained in the same way by changing the voltage on the auxiliary electrode 3 in such a way that the voltage of the electric field in the dielectric is kept close to zero. The device allows to improve the identity and reproducibility of the characteristics by reducing the time drift and hysteresis and to improve the accuracy of measuring the concentration of ions. 2 Il.

The invention relates to a measurement technique, to the field of measuring the concentration of ions in electrolyte solutions, and can most effectively be used in analytical systems with a small sample volume.

The purpose of the invention is to increase the accuracy of measuring the concentration of ions in electrolyte solutions.

Figure 1 shows the structural diagram of the device; 2 shows the structure of the indicator and auxiliary transistors in the sensitive area. . .

A device for measuring the concentration of ions in electrolyte solutions contains indicator 1 and auxiliary 2 transistors and auxiliary electrode 3 placed in a controlled electrolyte solution 4 in the vessel 5, the first 6 and second 7 voltage sources, the source 8 current a, the reflector 9 current, operational amplifier 10, temperature compensation unit 11 and voltmeter 2.

The indicator 1 and auxiliary 2 transistors are located in the same semiconductor substrate 13 covered with a dielectric layer 14, and above the sensitive area 15 of the indicator transistor 1 is formed

.-

35

zo

Jq.

50

55

A thin dielectric layer (20 nm cd, 200 nm), and an LL sensitive area 1.6 of the auxiliary transistor 2 is a thick dielectric layer (d 1 μm). The choice of TOLINDIN dielectric layers above the auxiliary and indicator transistors is associated with the actual minimum dielectric thickness, which still works as a dielectric (20 nm) and which the existing technology allows to apply, and a thick layer of dielectric still allows the indicator transistor to work as an indicator, and provides a sufficient potential difference for negative feedback operation. The terminals of the substrate of the indicator 1 and auxiliary 2 transistors are connected to the common bus of the device.

The total area of the source 17 of the indicator 1. And the auxiliary 2 transistors are connected to the first output of the current source 8, the second output of which is connected to the output of the first voltage source 6 and the first input of the temperature compensation unit 1I, the second input of which is connected to the output of the second voltage source 7 the input of the current reflector 9, the first output of which is connected to the drain 18 of the indicator transistor 1 and inverting

the input of the operational amplifier 10, the non-inverting input of which is connected to the second output of the current reflector 9 and the drain 19 of the auxiliary transistor 2. The output of the operational amplifier 10 is connected to the auxiliary electrode 3 and the third input of the temperature compensation unit 1, the output of which is connected to the input of the voltmeter 12 .

The device works as follows.

Indicator 1 and auxiliary 2 transistors are included in such a way that they operate in bipolar mode. Such a mode is possible if the diffusion length of minority carriers in the substrate exceeds the distance between the source and drain regions, respectively, of the indicator 1 (regions 17 and 18) and auxiliary 2 (regions 17 and 19) transistors. When the indicator and auxiliary 2 transistors and auxiliary electrode 3 are immersed in the electrolyte solution under study with the concentration of the ion of interest, a potential jump occurs at the electrolyte – dielectric interface, the magnitude of which in accordance with the Nernst equation is

f | In a ;, (1)

n-q

where (- standard potential;

K is the Boltzmann constant;

T - absolute temperature;

n is the valence of the ion;

q is the electron charge. Materials such as 51zK4,, etc. can be used as dielectrics.

The arising electric field through a thin dielectric of the indicator transistor 1 affects the near-surface semiconductor region j changing the transfer coefficient of the indicator transistor 1. At the same time, the transfer coefficient of the auxiliary transistor 2 practically does not change, because as a result of the thick dielectric, the electric field is many times weakened. Due to the negative feedback loop, the voltage on the drains of the indicator 1 and the auxiliary 2 transistors is maintained in the same way by changing to -.-; the voltage on the auxiliary electrode 3 in such a way that the intensity of the electric field in the dielectric

g 0

5 0 5 0

five

0

five

0

five

maintained close to zero. The output voltage of the op amp 10 is

and, about 0+,. h-EZ,, (2)

where E is the potential of the auxiliary electrode relative to the volume of the solution.

From the expression (2) it can be seen that the voltage does not depend on the parameters of the indicator 1 and auxiliary 2 transistors. The temperature compensation unit 1 compensates, similarly to the known device, the temperature dependence of the voltage at the output of the operational amplifier 10. Voltmeter 12 registers voltage changes proportional to changes in the logarithm of the concentration of the investigated ion in the electrolyte solution.

All blocks used in the device are known. In particular, the current reflector 9 can be made either in a manner similar to a fy device or on a pair of bipolar transistors. The temperature compensation unit I1 can be made in the same way as a known device. Any second electrode, such as Ag / AgCl, can be used as an auxiliary electrode.

The device allows to significantly improve the identity and reproducibility of the characteristics by reducing the time drift and hysteresis, and ensures the minimum temperature dependence of the output signal. By reducing the low-frequency noise, a metrological indicator such as the detection limit is improved.

Claims (1)

Invention Formula A device for measuring the concentration of ions in electrolyte solutions, containing an indicator transistor and an auxiliary electrode placed in a controlled electrolyte solution placed in a vessel, is an auxiliary transistor whose source is connected to the source of the indicator transistor and the first, the output of the current generator, the second output of which is connected to the output of the first voltage source and the first input of the temperature compensation unit, the second input of which connected to the output of the second voltage source and the input of the current reflector, the first output of which is connected to the drain of the indicator transistor and the inverting input of the operational amplifier, the non-inverting input of which is connected to the second output of the current reflector and the drain of the auxiliary transistor, the substrate of which is connected to the substrate of the indicator transistor, the output of the operating the amplifier is connected to the third input of the temperature compensation unit, the output of which is connected to the input of a voltmeter, / 5/5/7 J6 19 lif FIG. 2 characterized in that, in order to increase measurement accuracy, a dielectric layer without a metal gate electrode, whose thickness is 5-50 times greater than the thickness of the dielectric layer of the indicator transistor, is formed over the sensitive area of the auxiliary transistor, which is 5-50 times the thickness of the indicator transistor; the transistor is connected to the common bus device, and the output of the operational amplifier is connected to the auxiliary electrode.