JP6891658B2 - Sensor transistor drive circuit - Google Patents

Description

The techniques disclosed herein relate to drive circuits for sensor transistors.

Sensor transistors have been developed that are configured to output electrical signals based on channel resistance that changes depending on the measurement target. For example, Patent Document 1 discloses a sensor transistor that detects a target biomolecule contained in a sample solvent arranged on an insulated gate portion. In this sensor transistor, probe biomolecules that specifically bind to target biomolecules are fixed to the surface of the insulated gate. When the target biomolecule is bound to the probe biomolecule, the channel resistance of the sensor transistor changes depending on the charge of the target molecule. In this sensor transistor, the target biomolecule can be detected by measuring the change in the channel resistance. Further, Patent Document 2 discloses a sensor transistor for measuring the pH of a sample solvent arranged on an insulated gate portion. In this sensor transistor, the gate insulating film acts as an ion-sensitive film, and the channel resistance of the sensor transistor changes depending on the pH of the sample solvent. In this sensor transistor, the pH of the sample solvent can be measured by measuring the change in the channel resistance.

Japanese Unexamined Patent Publication No. 2007-304089 Japanese Unexamined Patent Publication No. 2012-202864

In these sensor transistors, for example, a reference electrode fixed at the ground potential is immersed in a sample solvent, and a fixed power supply is connected between the reference electrode and the base electrode of the sensor transistor. As a result, the voltage between the reference electrode and the base electrode of the sensor transistor is initially set to the voltage of the fixed power supply. However, even if the voltage between the reference electrode and the base electrode of the sensor transistor is initially set in this way, the region intended for the sensor transistor (for example, the threshold voltage, etc.) due to the performance variation of the sensor transistor (for example, the threshold voltage) There may be situations where it cannot be operated in the linear region). As a result, the reliability of the performance of the sensor transistor deteriorates. The present specification provides a technique for improving the reliability of the performance of a transistor for a sensor.

The present specification discloses a drive circuit of a sensor transistor in which a sample solvent is arranged on an insulating gate and a reference electrode is immersed in the sample solvent. The transistor for a sensor disclosed in the present specification is used for various purposes, and the use is not particularly limited. For example, a sensor transistor can be used for the purpose of observing the activity of cells in a sample solvent. Further, the sensor transistor can be used for the purpose of detecting the target biomolecule in the sample solvent by fixing the probe biomolecule on the insulating gate portion. This drive circuit may include a voltage adjusting circuit unit that adjusts the voltage between the reference electrode and the base electrode of the sensor transistor. The voltage adjustment circuit unit is configured to negatively feedback control the voltage between the reference electrode and the base electrode of the sensor transistor so that the output voltage of the sensor transistor matches the set voltage prior to the actual measurement. There is. By such negative feedback control, the output voltage of the sensor transistor can match the set voltage, that is, the initial voltage. As a result, even if there are variations in the performance of the sensor transistor (for example, the threshold voltage), it is possible to guarantee that the sensor transistor operates in the intended region (for example, the linear region), and the performance of the sensor transistor is reliable. The sex can be improved.

The material of the reference electrode may be copper or aluminum. In order to stabilize the potential of the sample solvent, it is desirable that, for example, silver or platinum, which is an inert material for ions in the sample solvent, is used for the reference electrode. However, such materials are expensive and increase the cost of sensor transistors. On the other hand, the drive circuit disclosed in the present specification is negative feedback control even when the output voltage of the sensor transistor fluctuates as a result of the reference electrode reacting with the ions in the sample solvent and the potential of the sample solvent fluctuates. Therefore, the output voltage of the sensor transistor can be corrected prior to the actual measurement. In other words, the drive circuit disclosed herein can allow the use of a reference electrode material, copper or aluminum, that reacts with ions in the sample solvent. As described above, the drive circuit disclosed in the present specification can be suitably used for a sensor transistor provided with an inexpensive reference electrode.

The voltage adjustment circuit unit may have an adjustment transistor connected between the reference electrode and the base electrode of the sensor transistor. The voltage adjustment circuit unit is configured to negatively feedback control the voltage between the reference electrode and the base of the sensor transistor by controlling the gate voltage of the adjustment transistor.

The outline of the cross-sectional view of the main part of the transistor for a sensor is shown. The circuit configuration connected to the sensor transistor is shown.

FIG. 1 shows a sensor transistor 10 for observing the state of cell activity. The sensor transistor 10 includes a silicon substrate 20, a base electrode 32, a source electrode 34, a drain electrode 36, an insulating film 37, a gate insulating film 38, a container 42, and a reference electrode 44.

The silicon substrate 20 has a p-type drift region 22, an n ⁺ -type source region 24, and an n ⁺ -type drain region 26. The source region 24 and the drain region 26 are provided on the surface layer portion of the silicon substrate 20, and are arranged apart from each other. A part of the drift area 22 is arranged between the source area 24 and the drain area 26, and a part of the drift area 22 is particularly referred to as a channel area CH.

The base electrode 32 covers the back surface of the silicon substrate 20 and is in contact with the drift region 22. The source electrode 34 covers a part of the surface of the silicon substrate 20 and is in contact with the source region 24. The drain electrode 36 covers a part of the surface of the silicon substrate 20 and is in contact with the drain region 26.

The insulating film 37 covers a part of the surface of the silicon substrate 20, and is arranged between the source electrode 34 and the drain electrode 36. In other words, an opening is formed in a part of the insulating film 37, the source electrode 34 contacts the source region 24, and the drain electrode 36 contacts the drain region 26 through the opening. The gate insulating film 38 covers a part of the surface of the silicon substrate 20 and is in contact with the channel region CH. The thickness of the gate insulating film 38 is, for example, 0.5 to 5 nm. The material of the gate insulating film 38 is, for example, silicon oxide (SiO ₂ ), hafnium oxide (HfO ₂ ) or zinc peroxide (ZnO ₂ ). As described above, the silicon substrate 20 is configured with an n-type channel MOSFET.

The container 42 is provided on the insulating film 37 so as to go around the gate insulating film 38, and has a tubular shape. One end of the container 42 is fixed to the surface of the insulating film 37, and defines a space for filling the culture solution 52. A plurality of cells are adhered to the surface 38a of the gate insulating film 38. The culture solution 52 is an example of the sample solvent disclosed in the present specification.

The reference electrode 44 is arranged by immersing it in the culture solution 52 filled in the container 42. The material of the reference electrode 44 is a chemically stable inert material, for example silver or platinum is used. The reference electrode 44 is fixed to the ground potential.

When the cells adhering to the surface 38a of the gate insulating film 38 are activated by receiving a specific stimulus, the ion channels of the biological membrane of the cells are opened and the ions contained in the culture solution 52 flow into the cells, and the cells of the cells The membrane potential changes. As a result, the channel resistance of the channel region CH changes. In the sensor transistor 10, this change in channel resistance is measured as a change in output voltage. In this way, the sensor transistor 10 can observe the state of cell activity.

FIG. 2 shows a drive circuit 100 connected to the sensor transistor 10. The drive circuit 100 includes a voltage follower circuit unit 60 and a voltage adjusting circuit unit 70. Here, "B" in the figure corresponds to the base electrode 32 and the source electrode 34 of the sensor transistor 10 shown in FIG. 1, and "D" in the figure corresponds to the drain electrode 36 of the sensor transistor 10 shown in FIG. Corresponding, "G" in the figure corresponds to the reference electrode 44 shown in FIG. The drain electrode 36 (D) of the sensor transistor 10 is connected to the positive electrode terminal of the power supply via the first resistance element R1, and the base electrode 32 (B) of the sensor transistor 10 is connected via the second resistance element R2. It is connected to the negative electrode terminal of the power supply. The first resistance element R1 and the sensor transistor 10 form a voltage dividing circuit, and the first output voltage V _OUT1 is output from the intermediate node thereof. The first output voltage V _OUT1 is impedance-converted by the voltage follower circuit unit 60, and is output to the output terminal as _{the second output voltage V OUT2.}

The voltage adjustment circuit unit 70 includes a comparator 71, a counter circuit 72, a latch circuit 73, a DA converter 74, an adjustment transistor 75, and a second resistance element R2. The comparator 71 is configured such that the first output voltage V _{OUT1 is input to the non-inverting input terminal, the set voltage V REF} is input to the inverting input terminal, and the output terminal is connected to the counter circuit 72. When the output signal of the comparator 71 is low, the counter circuit 72 counts up in synchronization with the clock signal CLK and outputs an N-bit first digital signal D1 indicating the counter value. The latch circuit 73 holds the first digital signal D1 of the counter circuit 72 when the output signal of the comparator 71 is switched from low to high. As will be described later, the latch circuit 73 outputs the second digital signal D2 corresponding to the first digital signal D1 to be held to the DA converter 74 in the actual measurement mode. The DA converter 74 inputs the first digital signal D1 or the second digital signal D2, converts the first digital signal D1 or the second digital signal D2 into the adjustment voltage _VA of the analog signal, and adjusts the transistor 75. Output to the gate of. The adjusting transistor 75 is an n-type channel MOSFET, and is connected between the reference electrode 44 (G) and the base electrode 32 (B) of the sensor transistor 10. Further, the adjusting transistor 75 and the second resistance element R2 are connected in series between the reference electrode 44 (G) and the negative electrode terminal of the power supply to form a voltage dividing circuit. The intermediate node of this voltage dividing circuit is connected to the base electrode 32 (B) of the sensor transistor 10.

Next, the operation of the drive circuit 100 will be described. The drive circuit 100 operates in two modes, a voltage adjustment mode and an actual measurement mode. The voltage adjustment mode is implemented prior to the actual measurement mode. First, in the voltage adjustment mode, the counter value of the first digital signal D1 of the counter circuit 72 is reset to "0" or a predetermined value, and the adjustment voltage VA output by the DA converter 74 is adjusted to be small. Therefore, the adjusting transistor 75, which is an n-type channel MOSFET, has a high resistance. As a result, the voltage between the reference electrode 44 (G) and the base electrode 32 (B) of the sensor transistor 10 becomes large, and the sensor transistor 10 is adjusted to a low resistance. As a result, the first output voltage V _OUT1 of the sensor transistor 10 is adjusted to be small. Therefore, since the comparator 71 outputs low, the counter circuit 72 counts up in synchronization with the clock signal CLK. When the first digital signal D1 of the counter circuit 72 increases, the adjustment voltage _VA output by the DA converter 74 also increases, and the first output voltage V _OUT1 of the sensor transistor 10 increases accordingly. When the first output voltage V _OUT1 of the sensor transistor 10 reaches the set voltage V _REF , the output signal of the comparator 71 is switched from low to high, the count-up of the counter circuit 72 is stopped, and the latch circuit 73 is the first digital signal. Latch D1 and end the voltage adjustment mode. As described above, in the voltage adjustment mode, the negative feedback control is performed so that _{the V OUT} 1 of the sensor transistor 10 matches the set voltage V _REF.

Next, after the voltage adjustment mode is completed, the actual measurement mode is executed. In the actual measurement mode, the operation of the counter circuit 72 is stopped, and the second digital signal D2 of the latch circuit 73 is input to the DA converter 74. _{The DA converter 74 inputs the adjustment voltage VA} corresponding to the second digital signal D2 to the gate of the adjustment transistor 75. In the actual measurement mode, the adjustment voltage _VA is applied to the gate of the adjustment transistor 75.

It is desired that the sensor transistor 10 is guaranteed to operate in, for example, a linear region in the actual measurement mode. On the other hand, the sensor transistor 10 includes performance variations (for example, threshold voltage and the like). For example, when the threshold voltage of the sensor transistor 10 becomes higher than the design value, the sensor determines that the voltage between the reference electrode 44 and the base electrode 32 (B) of the sensor transistor 10 is a predetermined fixed value. There is a concern that the transistor 10 will operate in the saturation region. However, the drive circuit 100 performs a voltage adjustment mode prior to the actual measurement mode, performs negative feedback control so that _{the first output voltage V OUT1} of the sensor transistor 10 matches the set voltage V _{REF, and controls the reference electrode.} The voltage between 44 and the base electrode 32 (B) of the sensor transistor 10 is corrected to a relatively high value. This guarantees that the sensor transistor 10 operates in the linear region even when the threshold voltage of the sensor transistor 10 becomes higher than the design value. As described above, according to the above-mentioned drive circuit 100, it is possible to correct the performance variation of the sensor transistor 10 and guarantee that the sensor transistor 10 operates in the linear region, and the reliability of the performance of the sensor transistor 10 can be guaranteed. Is improved.

Further, the drive circuit 100 can correct the performance variation of the reference electrode 44 and guarantee that the sensor transistor 10 operates in the linear region. The reference electrode 44 includes performance variations related to its impedance and capacitance components. As a result, the potential of the culture solution 52 in which the reference electrode 44 is immersed may vary depending on the sensor transistor 10, and the sensor transistor 10 may not be able to operate in the intended linear region. Even in such a case, the negative feedback control of the drive circuit 100 can guarantee that the sensor transistor 10 operates in the linear region.

Further, in the above embodiment, the material of the reference electrode 44 is silver or platinum, which is a chemically stable inert material. Instead of this example, the reference electrode 44 may be a cheaper material, aluminum or copper. When the reference electrode 44 made of aluminum or copper is used, the reference electrode 44 reacts with the ions in the culture solution 52 to fluctuate the potential of the culture solution 52. By executing the voltage adjustment mode prior to the actual measurement mode, the drive circuit 100 can suppress such fluctuations in the potential of the culture solution 52. In other words, the drive circuit 100 can allow the use of a reference electrode 44 material, copper or aluminum, that reacts with ions in the culture solution 52. As described above, the drive circuit 100 can be suitably used for the sensor transistor 10 provided with the inexpensive reference electrode 44.

Although specific examples of the present invention have been described in detail above, these are merely examples and do not limit the scope of claims. The techniques described in the claims include various modifications and modifications of the specific examples illustrated above. In addition, the technical elements described in the present specification or the drawings exhibit technical usefulness alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the techniques illustrated in the present specification or drawings can achieve a plurality of purposes at the same time, and achieving one of the purposes itself has technical usefulness.

10: Transistor for sensor, 20: Silicon substrate, 22: Drift region, 24: Source region, 26: Drain region, 32: Base electrode, 34: Source electrode, 36: Drain electrode, 37: Insulating film, 38: Gate insulation Membrane, 42: Container, 44: Reference electrode, 52: Culture solution, 60: Voltage follower circuit, 70: Voltage adjustment circuit, 71: Comparator, 72: Counter circuit, 73: Latch circuit, 74: DA converter, 75: Adjustment transistor, 100: Drive circuit

Claims (3)

A drive circuit for a sensor transistor used in which a sample solvent is placed on an insulated gate and a reference electrode is immersed in the sample solvent.
It is provided with a voltage adjustment circuit unit that adjusts the voltage between the reference electrode and the base electrode of the sensor transistor.
Prior to the actual measurement, the voltage adjusting circuit unit adjusts the voltage between the reference electrode and the base electrode of the sensor transistor so that the output voltage of the sensor transistor matches the set voltage. The drive circuit that is configured. The drive circuit according to claim 1, wherein the material of the reference electrode is copper or aluminum. The voltage adjustment circuit unit has an adjustment transistor connected between the reference electrode and the base electrode of the sensor transistor.
The voltage adjusting circuit unit is configured to adjust the voltage between the reference electrode and the base electrode of the sensor transistor by controlling the gate voltage of the adjusting transistor, according to claim 1 or 2. The drive circuit according to 2.

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