CN112082624A - A liquid level detection device and detection method thereof - Google Patents

Abstract

The invention discloses a liquid level detection device and a detection method thereof, wherein the liquid level detection device comprises: a transparent substrate; a light emitting diode, which is arranged on a first side of the transparent substrate and is used for emitting detection light; a photodiode , disposed on the first side of the transparent substrate, for receiving the detection light reflected from the second side surface of the transparent substrate; wherein, a second side surface of the transparent substrate and the air are formed an interface; the first interface has a first critical angle; the incident angle of the detection light on the second side surface of the transparent substrate is greater than the first critical angle. The technical scheme provided by the present invention solves the problems of large volume and low integration degree of the existing liquid level detection device.

Description

A liquid level detection device and detection method thereof

technical field

The invention relates to the technical field of semiconductors, and in particular, to a liquid level detection device and a detection method thereof.

Background technique

Existing liquid level photoelectric detectors have a variety of production methods. According to the principle, most of them use the detection method in which the transmitting tube and the receiving tube appear in pairs for detection. The transmitting tube can emit detection light, and the detection light passes through the liquid. Refraction or reflection reaches the receiving tube. Compared with the detection light that does not pass through the liquid to reach the receiving tube, the detection light received by the receiving tube will change, so as to achieve the purpose of detecting the liquid level of the liquid.

However, in the prior art, the liquid level photoelectric detector needs to seal the transmitting tube, the receiving tube and the prism for reflecting and detecting light into a whole device, which is relatively large in size and low in integration, and is not suitable for small devices Liquid level measurement.

SUMMARY OF THE INVENTION

The embodiments of the present invention provide a liquid level detection device and a detection method thereof, so as to solve the problems of large volume and low integration degree of the existing liquid level detection device.

In a first aspect, an embodiment of the present invention provides a liquid level detection device, including: a transparent substrate;

a light-emitting diode, disposed on the first side of the transparent substrate, for emitting detection light;

a photodiode, disposed on the first side of the transparent substrate, for receiving the detection light reflected by the surface of the second side of the transparent substrate;

Wherein, a first interface is formed between the second side surface of the transparent substrate and the air; the first interface has a first critical angle; the incident angle of the detection light on the second side surface of the transparent substrate greater than the first critical angle.

In the second aspect, the embodiment of the present invention also provides a liquid level detection method, which is applicable to the liquid level detection method provided by any embodiment of the present invention, including:

The liquid level detection device is placed in an air environment, and the light-emitting diode is controlled to emit detection light, so that the photodiode receives the detection light that is totally reflected by the first interface between the second side surface of the transparent substrate and the air, and records the detection light. the first current value formed by the photodiode;

The transparent substrate of the liquid level detection device is placed in the measurement environment of the liquid to be measured, and the light-emitting diode is controlled to emit detection light, so that the photodiode receives the light reflected by the second side surface of the transparent substrate. Detecting the light, and recording the photodiode to form a second current value;

If the difference between the first current value and the second current value is greater than the first set threshold value, it is determined that the liquid level of the liquid to be measured reaches the position of the liquid level detection device.

In the present invention, the liquid level detection device includes a light emitting diode and a photodiode formed on the first side of the same transparent substrate, the light emitting diode can emit detection light, and the photodiode can receive the side of the transparent substrate away from the light emitting diode (the second side ) The detection light reflected by the surface is set to form a first interface between the second side surface of the transparent substrate and the air, and the first interface has a first critical angle. This embodiment controls the setting distance between the light-emitting diode and the photodiode , so that the incident angle of the detection light on the second side surface of the transparent substrate is greater than the first critical angle, so that in the air environment, the detection light is incident into the photodiode through total reflection, and the photocurrent generated by the photodiode is larger, and when After the second side surface of the transparent substrate is the liquid to be measured, the optical path of the detection light is affected and is not in a state of total reflection, the photoelectric current generated by the photodiode becomes smaller, and thus the liquid level of the liquid to be measured is judged. In this embodiment , the light-emitting diode and photodiode are integrated on the same substrate of the liquid level detection device at the same time, and the integration degree is high. Compared with the scheme of integrating independent light-emitting diode elements and photodiodes in the same device, the overall size of the liquid level detection device is effectively reduced. It can be used for both large and small equipment, and improves the applicability of liquid level detection devices. In addition, the substrate is a transparent substrate, which can be used as a reflection interface for detecting light, and no additional prisms are required. The volume of the liquid level detection device is reduced, and the integration degree is improved.

Description of drawings

1 is a schematic structural diagram of a liquid level detection device provided by an embodiment of the present invention;

2 is a schematic diagram of a total reflection phenomenon provided by an embodiment of the present invention;

3 is a schematic structural diagram of a liquid level detection device located in an air environment provided by an embodiment of the present invention;

4 is a schematic structural diagram of a liquid level detection device located in a liquid environment to be measured according to an embodiment of the present invention;

5 is a schematic structural diagram of another liquid level detection device provided by an embodiment of the present invention;

6 is a schematic flowchart of a liquid level detection method provided by an embodiment of the present invention;

7 is a schematic structural diagram of a liquid level detection device provided in an embodiment of the present invention in a liquid measurement environment to be measured;

8 is a schematic structural diagram of another liquid level detection device provided in an embodiment of the present invention in a liquid measurement environment to be measured;

9 is a schematic structural diagram of another liquid level detection device provided in an embodiment of the present invention in a liquid measurement environment to be measured;

FIG. 10 is a schematic structural diagram of a liquid level detection device provided in an embodiment of the present invention in a microfluidic measurement environment.

Detailed ways

The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, but not to limit the present invention. In addition, it should be noted that, for the convenience of description, the drawings only show some but not all structures related to the present invention.

An embodiment of the present invention provides a liquid level detection device, comprising: a transparent substrate;

a light-emitting diode, disposed on the first side of the transparent substrate, for emitting detection light;

a photodiode, disposed on the first side of the transparent substrate, for receiving the detection light reflected by the surface of the second side of the transparent substrate;

Wherein, a first interface is formed between the second side surface of the transparent substrate and the air; the first interface has a first critical angle; the incident angle of the detection light on the second side surface of the transparent substrate is greater than the first critical angle.

It should be noted that the interface formed between the second side surface of the transparent substrate and the air is the first interface. If the second side surface of the transparent substrate is in contact with other environments, such as liquid, solid, etc., the transparent substrate The interface between the second side surface of the bottom and other environments is not the above-mentioned first interface. For example, the interface between the second side surface of the transparent substrate and the liquid to be tested is the second interface, and each interface corresponds to a critical interface. The above-mentioned first critical angle is the critical angle in the air environment before the liquid level detection device measures the liquid to be measured.

In the embodiment of the present invention, the liquid level detection device includes a light emitting diode and a photodiode formed on the first side of the same transparent substrate, the light emitting diode can emit detection light, and the photodiode can receive the side of the transparent substrate far away from the light emitting diode (No. The detection light reflected by the two sides) surface, the first interface is set between the second side surface of the transparent substrate and the air, and the first interface has a first critical angle. This embodiment controls the light emitting diode and the photodiode. The distance is set so that the incident angle of the detection light on the second side surface of the transparent substrate is greater than the first critical angle, so that in the air environment, the detection light is incident into the photodiode through total reflection, and the photocurrent generated by the photodiode is larger, When the second side surface of the transparent substrate is the liquid to be tested, and the optical path of the detected light is affected and is not in a state of total reflection, the photocurrent generated by the photodiode becomes smaller, thereby judging the liquid level of the liquid to be tested. In the example, a light-emitting diode and a photodiode are integrated on the same substrate of the liquid level detection device, and the integration degree is high. Compared with the scheme of integrating independent light-emitting diode elements and photodiodes in the same device, the liquid level detection device is effectively reduced. The overall size of the device can save production costs, and it can be applied to both large and small equipment, improving the applicability of the liquid level detection device. In addition, the substrate is a transparent substrate, which can be used as a reflection interface for detecting light, and no additional prisms are required. , further reducing the volume of the liquid level detection device and improving the integration.

The above is the core idea of the present invention, and the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present invention.

FIG. 1 is a schematic structural diagram of a liquid level detection device provided by an embodiment of the present invention. As shown in FIG. 1 , the liquid level detection device includes a transparent substrate 11 on which a light-emitting diode 12 and a photodiode are integrated at the same time. 13. The transparent substrate 11 includes an opposite first side and a second side, the light emitting diode 12 and the photodiode 13 are simultaneously arranged on the first side of the transparent substrate 11, and the light emitting diode 12 can emit detection light for detecting the liquid to be tested , the photodiode 13 is used to receive the detection light reflected from the second side surface of the transparent substrate 11, and the photodiode 13 judges whether the second side surface of the transparent substrate 11 is in contact with the air environment or the air environment through the change of the photocurrent generated by itself. The liquid environment to be tested. It should be noted that, because the second side surface of the transparent substrate 11 is used as a reflection surface or a refraction surface for the detection light, in order to avoid the influence of the substrate on the transmission of the detection light, the substrate must be the transparent substrate 11. Preferably, Its transparency is high, and it hardly causes the optical path loss of the detection light in the transmission process. Optionally, in this embodiment, the material of the transparent substrate 11 may be at least one of sapphire, silicon carbide and silicon. Among them, sapphire (alumina) substrate is the preferred substrate for making light-emitting diode chips. Sapphire substrate has mature production technology, good quality, good stability, high mechanical strength and easy cleaning. The silicon carbide substrate has good thermal conductivity, which effectively enhances the heat dissipation of components. The silicon substrate also has good thermal conductivity, which effectively prolongs the life of components.

As shown in FIG. 2, FIG. 2 is a schematic diagram of a total reflection phenomenon provided by an embodiment of the present invention. The critical angle refers to the interface between the optically denser medium and the optically sparser medium, when the light enters the optically sparser medium from the optically denser medium. , if the light is just at the angle at which the total reflection phenomenon occurs, when the incident angle θ1 of the light is greater than the above critical angle, all the light is totally reflected and cannot be incident on the optically sparser medium. 3 is a schematic structural diagram of a liquid level detection device in an air environment provided by an embodiment of the present invention. In this embodiment, it is assumed that a first interface S1 is formed between the second side surface of the transparent substrate 11 and the space, and the transparent substrate 11 Air is an optically dense medium, and air is an optically sparser medium. The first interface S1 has a first critical angle α1. When the incident angle of the detection light L1 is greater than the first critical angle α1, the detection light L1 will undergo total reflection. Then, by setting the distance d1 between the light-emitting diode 12 and the photodiode 13, the detection light L1 emitted from the light-emitting diode 12 is incident on the photodiode 13 after total reflection on the second side surface of the transparent substrate 11, that is, so that The incident angle of the detection light L1 on the second side surface of the transparent substrate 11 is greater than the first critical angle α1 .

4 is a schematic structural diagram of a liquid level detection device located in an environment of a liquid to be tested provided by an embodiment of the present invention, and when the liquid level detection device is placed in the environment of the liquid to be tested, for example, the second side of the transparent substrate 11 When the surface is in contact with or immersed in the liquid to be measured, a second interface S2 will be formed between the transparent substrate 11 and the liquid to be measured. 11 is an optically dense medium, and the liquid to be tested is an optically sparser medium, then the second critical angle of the second interface S2 is different from the above-mentioned first critical angle α1, and the detection light incident on the photodiode 13 will also change, for example As shown in FIG. 4 , when the incident angle of the detection light L1 is α1, total reflection does not occur at the second interface S2, and some detection light may be refracted into the liquid to be tested, then the detection light received by the photodiode 13 is less, so that the photodiode 13 generates a small current value. In this embodiment, the current generated by the photodiode 13 is monitored in real time. If the photodiode 13 detects a sudden change in the current or a large change in the current, it means that the liquid to be tested is The level reaches the position of the liquid level detection device.

Optionally, the thickness of the transparent substrate 11 may range from 100 μm to 200 μm, which is convenient for the detection light to enter the photodiode 13 after total reflection on the second side surface of the transparent substrate 11 , providing a certain space for the total reflection optical path of the detection light. , the thickness of the transparent substrate 11 is greater than or equal to 100 μm. In addition, in order to realize the miniaturization of the entire liquid level detection device, the transparent substrate 11 should not be too thick, and its thickness may be less than or equal to 200 μm. Optionally, the thickness of the transparent substrate 11 can be selected to be 150 μm.

In this embodiment, the transparent substrate is used as the emission interface of the light-emitting diode, and there is no need to set up a reflective prism to reduce the volume of the liquid level detection device. Realize the miniaturization of the liquid level detection device. The liquid level detection device in this embodiment can be applied to smaller liquid containers to be tested, for example, can be applied to small equipment such as water dispensers and water purifiers. It can even be applied to miniaturized equipment. The above-mentioned liquid level detection device can be arranged on a microfluidic pipeline, so that the liquid level detection or liquid composition analysis of the liquid to be measured in the microfluidic pipeline can be performed.

FIG. 5 is a schematic structural diagram of another liquid level detection device provided by an embodiment of the present invention. Optionally, the light emitting diode 12 may include a first doping part 121 , a light emitting part 122 and a second doping part 121 , which are disposed away from the transparent substrate 11 in sequence. The doped part 123; the photodiode 13 includes a third doped part 131, a photoelectric conversion part 132 and a fourth doped part 133 which are arranged away from the transparent substrate 11 in sequence; the first doped part 121 and the third doped part 131 are the same The light emitting part 122 and the photoelectric conversion part 132 are arranged in the same layer; the second doping part 123 and the fourth doping part 133 are arranged in the same layer.

When forming the light-emitting diode 12 and the photodiode 13, the light-emitting diode 12 and the photodiode 13 can be fabricated at the same time. Specifically, the light-emitting diode 12 includes the first doping portion 121 and the light-emitting portion formed on the transparent substrate 11 in sequence. 122 and the second doping part 123 , the photodiode 13 includes a third doping part 131 , a photoelectric conversion part 132 and a fourth doping part 133 formed on the transparent substrate 11 in sequence. The first doping part 121 and the third doping part 131 can be provided in the same layer by the same process, the light emitting part 122 and the photoelectric conversion part 132 can be provided in the same layer by the same process, and the second doping part 123 and the fourth doping part 133 The same process can be used to provide the same layer, so as to realize the integration of the light emitting diode 12 and the photodiode 13 on the same substrate. There is no need to dispose the light emitting diode 12 and the photodiode 13 on two different chips respectively, which effectively saves the fabrication cost of the chips. The light emitting part 122 of the light emitting diode 12 may include multiple quantum wells, so that electrons and holes input from the first doping part 121 and the second doping part 123 of the light emitting diode 12 recombine in the light emitting part 122 to emit photons. The photoelectric conversion part 132 of the photodiode 13 may include a plurality of quantum wells, which can receive light radiation from the outside and generate an induced current, which is output to the external circuit by the third doping part 131 and the fourth doping part 133 of the photodiode 13 .

Optionally, the first doping portion 121 may be an N-type doping layer, the second doping portion 123 may be a P-type doping layer; the third doping portion 131 may be an N-type doping layer, and the fourth doping layer The portion 133 may be a P-type doped layer. Alternatively, the first doping portion 121 may be a P-type doping layer, the second doping portion 123 may be an N-type doping layer; the third doping portion 131 may be a P-type doping layer, and the fourth doping portion 133 It can be an N-type doped layer. Optionally, the N-type doped layer may be N-type doped gallium nitride, and the P-type doped layer may be P-type doped gallium nitride.

Continuing to refer to FIG. 5 , optionally, an insulating layer 14 may be disposed between the light emitting diode 12 and the photodiode 13 ; the insulating layer 14 is a non-transparent material. In this embodiment, a non-transparent insulating layer 14 is formed between the light-emitting diode 12 and the photodiode 13, which can prevent the detection light emitted by the light-emitting diode 12 from directly irradiating the photodiode 13 and improve the photocurrent detection of the photodiode 13. Accuracy, and improve the light sensitivity of the entire liquid level detection device, improve the accuracy of liquid level measurement.

Optionally, the packaging method of integrating light-emitting diodes and photodiodes on a single substrate is more flexible. In this embodiment, the traditional front-mounted substrate bonding method, lead frame method, and flip-chip method can be used for packaging. Not limited to a single package.

Based on the same concept, the embodiment of the present invention also provides a liquid level detection method. FIG. 6 is a schematic flowchart of a liquid level detection method provided by an embodiment of the present invention. As shown in FIG. 6 , the method of this embodiment includes the following steps:

Step S110, placing the liquid level detection device in an air environment, and controlling the light-emitting diode to emit detection light, so that the photodiode receives the detection light that is totally reflected by the first interface between the second side surface of the transparent substrate and the air, and records the detection light. The first current value formed by the photodiode.

Step S120, placing the transparent substrate of the liquid level detection device in the measurement environment of the liquid to be measured, and controlling the light-emitting diode to emit detection light, so that the photodiode receives the detection light reflected by the second side surface of the transparent substrate, and records the photodiode A second current value is formed.

Step S130 , if the difference between the first current value and the second current value is greater than the first set threshold, determine that the liquid level of the liquid to be measured reaches the position of the liquid level detection device.

When the liquid level detection device does not detect the liquid level to be measured, the light-emitting diode is turned on so that the detection light is totally reflected, and the photodiode forms the first current value. The photodiode forms a second current value, and detects the difference between the first current value and the second current value. If the difference is almost zero, the second side surface of the transparent substrate forms a first interface with the air, and the test is to be detected. The liquid level of the liquid has not yet reached the height of the liquid level detection device. If the difference is greater than the first set threshold, it means that the second current value has changed abruptly, that is, the medium in contact with the second side surface of the transparent substrate A change occurs, the second side surface of the transparent substrate contacts the liquid to be tested to form a second interface, and the liquid level of the liquid to be tested is equal to or higher than the height of the current liquid level detection device. In this embodiment, when measuring the liquid level of the liquid to be measured, a plurality of liquid level detection devices can be evenly arranged along the vertical height direction, and the liquid to be measured is finally determined by the magnitude of the second current value output by each liquid level detection device. the liquid level height.

In the embodiment of the present invention, the liquid level detection device includes a light emitting diode and a photodiode formed on the first side of the same transparent substrate, and a first interface is formed between the second side surface of the transparent substrate and the air, and the first interface is set. There is a first critical angle at the interface. In this embodiment, the distance between the light-emitting diode and the photodiode is controlled, so that the incident angle of the detection light on the second side surface of the transparent substrate is greater than the first critical angle, so that in an air environment, the detection The light is incident into the photodiode through total reflection, and the first current value generated by the photodiode is relatively large, and when the second side surface of the transparent substrate is the measurement environment of the liquid to be measured, the photodiode generates a second current value. The second side surface of the bottom is in contact with the liquid to be tested to form a second interface, and the optical path of the detection light is affected and is not in a state of total reflection, then the second current value generated by the photodiode is small, so it is judged that the liquid level of the liquid to be tested has reached or exceeds the height of the liquid level detection device. In this embodiment, light emitting diodes and photodiodes are simultaneously integrated on the same substrate of the liquid level detection device, and the integration degree is relatively high. Compared with the integration of independent light emitting diode elements in the same device The solution with photodiode can effectively reduce the overall size of the liquid level detection device, save the production cost, can be applied to both large and small equipment, and improve the applicability of the liquid level detection device. In addition, the substrate is a transparent substrate, which can be As a reflection interface for detecting light, an additional prism needs to be installed, which further reduces the volume of the liquid level detection device and improves the integration.

FIG. 7 is a schematic structural diagram of a liquid level detection device provided in an embodiment of the present invention in a liquid measurement environment to be measured, and FIG. 8 is a schematic structural diagram of another liquid level detection device provided in an embodiment of the present invention in a liquid measurement environment to be measured. , Optionally, as shown in FIG. 7 , the measurement environment of the liquid to be tested can be the inner side of the side wall of the container in which the liquid to be tested 3 is placed; the transparent substrate 11 is used for contacting the liquid to be tested 3; or, as shown in FIG. 8 , the measurement environment of the liquid to be tested may be the outer side of the transparent side wall of the container in which the liquid to be tested 3 is placed; the transparent substrate 11 is attached to the outer side of the transparent side wall 2 .

The measurement environment of the liquid to be measured in this embodiment may be an environment that can be in direct contact with the liquid to be measured. As shown in FIG. 7 , the transparent substrate 11 of the liquid level detection device may be disposed on the side wall 2 of the container of the liquid to be measured 3 . inside, so that the second side surface of the transparent substrate 11 can directly contact the liquid to be measured, so as to measure the liquid level of the liquid to be measured. Figure 7 shows the structure in which the liquid level detection device passes through the side wall 2. This In the embodiment, the entire liquid level detection device can also be sealed and packaged and placed in the liquid to be measured, as shown in FIG. 9 , which is a structure of another liquid level detection device provided in the embodiment of the present invention in the measurement environment of the liquid to be measured. In the schematic diagram, the liquid level detection device 1 is directly immersed in the liquid 3 to be tested, and because the detection device 1 can be fixed on the side wall 2 . In this embodiment, the liquid to be tested may be water, oil, chemical reagent, etc., which is not limited in this embodiment.

Except for the solution in which the second side surface of the transparent substrate 11 is directly in contact with the liquid 3 to be tested, in this embodiment, the transparent substrate 11 may not be in contact with the liquid to be tested 3 . As shown in FIG. 8 , if the container containing the liquid to be tested 3 is If the side wall 2 is made of transparent material, the second side surface of the transparent substrate 11 of the liquid level detection device can be attached to the side wall 2, and the liquid 3 to be tested can pass through the transparent side wall 2 and also affect the detection light in the transparent Reflection of the second side surface of the substrate 11 to detect the liquid level of the liquid to be measured. In this embodiment, when the liquid level to be measured 3 is detected, it does not directly contact the liquid to be measured 3, so that the liquid to be measured 3 will not be polluted. For example, if the liquid to be measured 3 is pure water in a water dispenser, the The second side surface of the transparent substrate 11 of the liquid level detection device is attached to the outer side of the transparent water bucket, so as to detect the liquid level of pure water.

Optionally, the liquid to be tested may be the liquid in the microfluidic pipeline. In this embodiment, the liquid level detection device can be miniaturized, and the miniaturized liquid level detection device can be applied to miniaturized equipment. The liquid to be tested in the pipeline is subjected to liquid level detection or liquid composition analysis. Specifically, as shown in FIG. 10, FIG. 10 is a schematic structural diagram of a liquid level detection device provided in an embodiment of the present invention in a microfluidic measurement environment. It can be seen that the size of the microfluidic pipeline 4 is extremely small, even smaller than that of the liquid level detection device. The chip size of the device 1 is smaller. Exemplarily, the diameter of the microfluidic tube 4 ranges from 100 μm to 800 μm. For example, the diameter of the microfluidic tube 4 is generally 400 μm. Then the miniaturized liquid level detection device 1 can be attached to the outer side wall of the microfluidic pipe 4, and the liquid level detection device 1 can measure whether the liquid to be measured flows in the microfluidic pipe 4, and can even further distinguish. Several different typical values of the refractive index of the detected light are obtained, so as to analyze the liquid composition of the liquid to be tested.

Note that the above are only preferred embodiments of the present invention and applied technical principles. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and various obvious changes, readjustments and substitutions can be made by those skilled in the art without departing from the protection scope of the present invention. Therefore, although the present invention has been described in detail through the above embodiments, the present invention is not limited to the above embodiments, and can also include more other equivalent embodiments without departing from the concept of the present invention. The scope is determined by the scope of the appended claims.

Claims (10)

1. A liquid level detection device, comprising: a transparent substrate;

the light emitting diode is arranged on the first side of the transparent substrate and used for emitting detection light;

the photodiode is arranged on the first side of the transparent substrate and used for receiving the detection light reflected by the surface of the second side of the transparent substrate;

wherein a first interface is formed between the second side surface of the transparent substrate and air; the first interface presents a first critical angle; the incident angle of the detection light ray on the second side surface of the transparent substrate is larger than the first critical angle.

2. The liquid level detection apparatus according to claim 1, wherein the light emitting diode includes a first doped portion, a light emitting portion, and a second doped portion disposed away from the transparent substrate in this order; the photodiode comprises a third doping part, a photoelectric conversion part and a fourth doping part which are sequentially far away from the transparent substrate;

the first doping part and the third doping part are arranged on the same layer; the light emitting section and the photoelectric conversion section are provided in the same layer; the second doping portion and the fourth doping portion are arranged on the same layer.

3. The liquid level detection device of claim 2, wherein the first doped portion is an N-type doped layer and the second doped portion is a P-type doped layer; the third doping part is an N-type doping layer, and the fourth doping part is a P-type doping layer.

4. The liquid level detection device of claim 2, wherein an insulating layer is disposed between the light emitting diode and the photodiode; the insulating layer is made of non-light-transmitting materials.

5. The liquid level detection apparatus of claim 2, wherein the material of the transparent substrate is at least one of sapphire, silicon carbide, and silicon.

6. The liquid level detection apparatus of claim 2, wherein the transparent substrate has a refractive index greater than a refractive index of the liquid to be measured.

7. The liquid level detection apparatus of claim 2, wherein the transparent substrate has a thickness in a range of 100 μm to 200 μm.

8. A liquid level detection method applied to the liquid level detection apparatus according to any one of claims 1 to 7, comprising:

placing the liquid level detection device in an air environment, controlling the light emitting diode to emit detection light, enabling the photodiode to receive the detection light totally reflected by a first interface between the second side surface of the transparent substrate and the air, and recording a first current value formed by the photodiode;

placing the transparent substrate of the liquid level detection device in a liquid measurement environment to be measured, controlling the light emitting diode to emit detection light, enabling the photodiode to receive the detection light reflected by the second side surface of the transparent substrate, and recording a second current value formed by the photodiode;

and if the difference value between the first current value and the second current value is greater than a first set threshold value, judging that the liquid level of the liquid to be detected reaches the position of the liquid level detection device.

9. The liquid level detection method according to claim 8, wherein the liquid measurement environment to be measured is outside a transparent sidewall of a container in which the liquid to be measured is placed; the transparent substrate is attached to the outer side of the transparent side wall; or,

the liquid to be measured is measured in the measuring environment, namely the inner side of the side wall of the container for placing the liquid to be measured; the transparent substrate is used for contacting with the liquid to be measured.

10. The liquid level detection method of claim 8, wherein the liquid to be detected is a liquid in a microfluidic pipeline.

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