Non-refrigeration infrared sensor based on semiconductor carbon nanotube film and preparation method thereof

Abstract

The invention discloses an uncooled infrared sensor based on a semiconductor carbon nanotube film and a preparation method thereof. The uncooled infrared sensor of a local bottom gate structure comprises a source electrode, a first electrode, a second electrode, a third electrode and a fourth electrode, a gate insulating layer; a substrate; a gate electrode; a drain electrode; provided is a semiconductive carbon nanotube thin film. According to the invention, the conjugated polymer material is adopted to prepare the carbon nanotubes (CNTs), the situation that the metallic carbon nanotubes form a high-conductivity path in the carbon nanotube film in the prior art is avoided, the overall resistance is reduced, the film resistance is more sensitive to temperature response after the metallic carbon nanotubes are removed, and uncooled infrared sensing at normal temperature can be realized. The thin-film resistor is regulated and controlled through a local bottom gate framework, the TCR (temperature coefficient of resistance) of the uncooled infrared sensor is improved, the defects of a traditional TCR regulation and control method are overcome, and the uncooled infrared sensor has the advantages of reversibility, accurate control and suitability for large-scale manufacturing and can be better used for measurement of a bolometer.

Description

Technical Field

[0001] The present invention belongs to the field of electronic technology, and further relates to an uncooled infrared sensor based on a semiconductor carbon nanotube film and a preparation method in the field of microelectronic technology. The present invention can be applied to uncooled infrared sensors and key materials of large-scale integrated circuits, obtain high-purity semiconductor carbon nanotubes through conjugated polymer sorting technology, and realize the regulation of film resistance through a local bottom gate architecture. Background Art

[0002] As the core component of uncooled infrared sensors, bolometers are widely used in infrared detection, imaging, thermal imaging and other fields. Their key role is to measure temperature or radiation intensity by sensing the heat changes radiated by an object. Vanadium oxide film has become a commonly used thermosensitive film material due to its high temperature coefficient of resistance (about -2% / ℃), which can effectively improve the sensitivity and response speed of the calorimeter. However, as a new material with excellent electrical conductivity and thermal conductivity, carbon nanotubes face challenges in the application of infrared sensing. Although carbon nanotubes have excellent electrical conductivity, their low semiconductor purity leads to a relatively low temperature coefficient of resistance, and they cannot replace the role of vanadium oxide film in bolometers, limiting their application prospects in improving the sensitivity of bolometers. In the prior art, the semiconductor purity of carbon nanotubes is low. The semiconductor purity of carbon nanotube solutions after sorting by gel chromatography is usually less than 99%. The presence of metallic carbon nanotubes will affect the temperature coefficient of resistance of the film.

[0003] NEC Corporation proposed a method for manufacturing infrared sensor materials in its patent document "Method for manufacturing infrared sensor materials, infrared sensor materials, infrared sensor materials, infrared sensor elements and infrared image sensors" (application number CN201180049497.0, application date 2011.09.01, application publication number CN 103153850 A, application publication date 2013.06.12). The method includes: preparing a CNT dispersion by dispersing carbon nanotubes (CNT) in a solvent, using the CNT dispersion as a raw material to form a CNT film, and annealing the CNT film so that the absolute value of the temperature coefficient of resistance is equal to or greater than 1% / K at a temperature of -10°C to 50°C, and successfully preparing a sensor suitable for infrared sensing. However, there are two shortcomings in this method. First, due to the strong dependence of semiconductor SWNTs on temperature, the overall temperature coefficient of resistance tends to be negative. However, the presence of metallic SWNTs will reduce the absolute value of the negative temperature coefficient of resistance, thereby affecting the overall electrical response characteristics of the film. Second, this method directly uses industrially produced carbon nanotubes (CNTs), which are usually a mixture of metallic and semiconducting carbon nanotubes. In this mixed system, semiconducting single-walled carbon nanotubes (SWNTs) have a negative temperature coefficient of resistance, while metallic SWNTs have a positive temperature coefficient of resistance. Therefore, in the SWNT film formed by the mixture of the two, as the temperature changes, the contribution of each component is different, resulting in a change in the overall temperature coefficient of resistance.

[0004] Huawei Technologies Co., Ltd. provides a carbon nanotube-based infrared sensor and single-walled carbon nanotube film in its patent application "Infrared sensor and single-walled carbon nanotube film based on carbon nanotubes" (application number CN 201710617436.9, application date 2017.07.26, application publication number CN 107576402A, application publication date 2018.01.12). The infrared sensor includes: a silicon substrate; a dielectric layer; a positive electrode and a negative electrode, the positive electrode and the negative electrode; a single-walled carbon nanotube film, the first end of the single-walled carbon nanotube film is in contact with the upper surface of the positive electrode, the second end of the single-walled carbon nanotube film is in contact with the upper surface of the negative electrode, and the first end and the second end are opposite; wherein the ratio between the peak height of the characteristic peak of the Raman spectrum of the single-walled carbon nanotube film and the peak height corresponding to the 280nm wavelength position of the Raman spectrum is greater than or equal to 3.5. The infrared sensor has a high detection efficiency. The single-walled carbon nanotube film uses single-walled carbon nanotubes as the basic raw material, and uses gel chromatography separation technology to sort the single-walled carbon nanotubes. In the process of film preparation, orientation treatment is carried out with the help of means such as the crystal phase template method, and finally the single-walled carbon nanotube film is successfully prepared. The film is suitable for infrared sensors and can be used as its key component. However, the disadvantage of this method is that although the purity of the semiconductor single-walled carbon nanotubes in the single-walled carbon nanotube film used in the current infrared sensor is relatively high, exceeding 80%, there are still certain defects. A small amount of amorphous carbon or metallic single-walled carbon nanotubes may be mixed in the film, and the presence of metallic single-walled carbon nanotubes will cause the absolute value of the overall resistance temperature coefficient to decrease, affecting the sensor performance. Summary of the invention

[0005] The purpose of the present invention is to provide a non-cooled infrared sensor based on a semiconductor single-walled carbon nanotube (SWNT) film and a method for preparing the same in view of the deficiencies in the above-mentioned prior art. The purpose is to solve the problem that the carbon nanotubes (CNTs) synthesized in the prior art are usually a mixture of metallic and semiconductor properties, while the infrared sensor mainly relies on the photoelectric response characteristics of semiconductor CNTs. If the content of metallic CNTs is high, parasitic conductive channels will be introduced into the sensor, reducing signal responsiveness and sensitivity, thereby affecting device performance. In addition, traditional resistance temperature coefficient control methods (such as doping, structural optimization or composite material design) usually have the following problems: irreversibility, poor environmental stability, difficulty in uniformity control, and complex batch manufacturing process.

[0006] The technical idea for achieving the purpose of the present invention is that the present invention uses conjugated polymers to sort semiconductor carbon nanotubes. Since there are π-π interactions and band alignment effects between conjugated polymers (such as P3HT, PFO-BPy) and semiconductor carbon nanotubes, semiconductor carbon nanotubes are preferentially coated and dispersed. After centrifugation, washing and deposition, a high-purity semiconductor carbon nanotube solution can be obtained for film preparation. Since semiconductor carbon nanotubes have a certain band gap (about 0.5-1eV), when the temperature rises, the concentration of thermally excited carriers increases, so that the conductivity changes significantly with temperature, thereby improving the temperature coefficient of resistance. Metallic carbon nanotubes have no band gap, and the conductivity is basically not affected by temperature changes. A high conductive path is formed in the carbon nanotube film to reduce the overall resistance. Therefore, after removing the metallic carbon nanotubes, the resistance of the film is more sensitive to temperature. By optimizing the structure of the polymer and the solution conditions, the purity of the semiconductor carbon nanotubes can reach more than 99%, which is much higher than traditional separation methods (such as centrifugation, gel chromatography, etc.). The higher the purity, the fewer parasitic conductive channels of metallic SWNTs in the final device, making the performance of electronic and optoelectronic devices more stable. This solves the problem that the Fermi level of metallic carbon nanotubes in the prior art does not match the conjugated polymer, resulting in a weak coating effect and making it easy to be removed during the solution sorting process. The present invention uses a local bottom gate architecture to control the film resistance and adjust the gate voltage to further optimize the film resistance, improve the temperature coefficient of resistance (TCR) of the sensor, and achieve a high TCR response for the measurement of the radiation thermometer. When a local bottom gate voltage (Vg) is applied, the Fermi level (E F ) moves: when a positive gate voltage (Vg>0) is applied, the Fermi level moves down, the hole concentration increases, and the conductivity of the film is improved; when a negative gate voltage (Vg<0) is applied, the Fermi level moves up, reducing the hole concentration and increasing the film resistance. By optimizing the gate voltage, the carbon nanotube film can be placed in a high TCR state, that is, its resistance is more sensitive to changes in temperature. Compared with traditional TCR control methods, local bottom gate technology has the advantages of reversibility, precise control and suitability for large-scale manufacturing.

[0007] To achieve the above-mentioned purpose, the uncooled infrared sensor based on the semiconductor carbon nanotube film of the present invention adopts the semiconductor carbon nanotube film as the thermistor layer, adjusts the gate voltage to control the thermistor film resistance through the local bottom gate device structure, and exhibits different resistance temperature coefficients under different gate voltages.

[0008] Furthermore, the local bottom-gate device structure includes a source electrode, a gate insulating layer, a substrate, a gate electrode, a drain electrode, and a semiconductor carbon nanotube film, which are prepared in sequence from bottom to top.

[0009] Furthermore, the channel length between the source and drain electrodes of the local bottom gate device is designed to be 20 μm, the electrode width is 100 μm, and the gate insulating layer 2 is made of HfO 2 The device has a thickness of 10 nm, and the source electrode, the gate electrode, and the drain electrode are all composed of 10 nm thick titanium (Ti) and 50 nm thick palladium (Pd) as metal layers (Ti / Pd). The source electrode, the gate electrode, and the drain electrode are all passed through the central axis of the overall device and are symmetrically arranged about the central axis. The central axis of the overall device refers to the central axis of the gate electrode.

[0010] Furthermore, the semiconductor carbon nanotube film is sorted using conjugated polymer materials.

[0011] Further, the conjugated polymer material is any one of poly[(9,9-dioctylfluorenyl-2,7-diyl)-alt(6,6′-{2,2′-bipyridine})](PFO-BPy), poly[(9,9-di-n-octylfluorenyl-2,7-diyl)-alt-(benzo[2,1,3]thiadiazole-4,8-diyl)](F8BT), poly(9,9-dioctyl-fluorenyl-2,7-diyl-pyridine-2,6-diyl))(PFP), (1-octanoyl)-9H-carbazole-2,7-diyl-alt-pyridine-2,6-diyl](PCP), poly(9,9-di-n-octylfluorenyl-2,7-diyl))(PFO), and poly[9-(1-octylnonyl)-9H-carbazole](PCZ).

[0012] Furthermore, the gate voltage is adjusted to control the thermistor film resistance, and different resistance temperature coefficients are exhibited under different gate voltages, which means that the prepared uncooled infrared sensor is a p-type device, the device is turned on under a negative gate voltage, and the resistance is small; the device is turned off under a positive gate voltage, and the resistance is large; under different gate voltages, the device exhibits different resistance temperature coefficients; under a positive gate voltage, the resistance of the device increases with increasing temperature, and at a gate voltage of 3V, the resistance temperature coefficient is about 3%, which is equivalent to vanadium oxide, and the semiconductor carbon nanotube film can be used for the measurement of a radiation thermometer; under a negative gate voltage, the resistance of the device decreases with increasing temperature, and the resistance temperature coefficient is about -0.1% at a gate voltage of -3V.

[0013] The invention discloses a method for preparing a non-refrigerated infrared sensor based on a semiconductor carbon nanotube film, which comprises sorting a semiconductor carbon nanotube film solution and generating a local bottom grid structure.

[0014] Furthermore, the steps of sorting the semiconductor carbon nanotube film solution are as follows: pre-centrifuge the dispersion for 30 minutes using a high-speed centrifuge, with an average centrifugal force of 20,000 g and a temperature controlled at 4°C to remove most of the impurities and metal tubes in the solution; collect 90% of the supernatant after the pre-centrifugation, perform a secondary centrifugation for 2 hours, with an average centrifugal force set to 50,000 g and a temperature controlled at 4°C, and finally take out 90% of the supernatant as a semiconductor carbon nanotube solution to complete the solution sorting.

[0015] Furthermore, a 10 nm thick hafnium oxide (HfO 2 ) initial dielectric layer; define the gate region using a photomask, sputter deposit a titanium / palladium (Ti 10nm / Pd 50nm) metal layer; prepare a 10nm thick HfO on the gate by PECVD 2 The gate dielectric layer is formed; the ohmic electrode area is defined by a photomask, and the Ti / Pd metal layer is repeatedly sputtered and deposited; a carbon nanotube network film is formed on the device surface by a dip coating method; the device is then electrically isolated by a photomask combined with plasma etching; the gate hole is opened by a photomask and fluorine-based etching, and finally a carbon nanotube network device with a local bottom gate structure is obtained.

[0016] Compared with the prior art, the present invention has the following advantages:

[0017] First, the present invention uses conjugated polymer materials to prepare carbon nanotubes (CNTs), avoiding the shortcomings of the prior art that metallic carbon nanotubes form high conductive paths in carbon nanotube films, reduce overall resistance, introduce parasitic conductive channels in sensors, reduce signal responsiveness and sensitivity, and thus affect device performance. Conjugated polymers and semiconducting carbon nanotubes produce π-π interactions and band alignment effects, thereby preferentially coating and dispersing semiconducting carbon nanotubes, so that after the present invention removes metallic carbon nanotubes, the film resistor responds more sensitively to temperature. It can realize the preparation of non-refrigerated infrared sensors at room temperature.

[0018] Second, in the thin film preparation method of the present invention, a high-purity semiconductor carbon nanotube solution is obtained through centrifugation, washing and deposition steps. By optimizing the structure of the polymer and the solution conditions, a high-purity single-walled carbon nanotube with a purity of more than 99% can be obtained. This technology relies on the solution treatment process and is compatible with solution processing techniques such as spraying, spin coating, and printing, and can be used for low-cost, large-area manufacturing. The traditional CVD selective growth method requires high temperature (600-900°C) and is difficult to be compatible with flexible electronic processes. However, conjugated polymer sorting can be carried out at room temperature or low temperature (<100°C), which is more suitable for organic electronic devices and flexible substrates.

[0019] Third, the present invention realizes the regulation of thin film resistance through a local bottom gate architecture to adjust the gate voltage to further optimize the thin film resistance, thereby improving the temperature coefficient of resistance (TCR) of the uncooled infrared sensor, overcoming the defects of traditional TCR regulation methods (such as doping, structural optimization or composite material design), such as poor environmental stability, difficulty in uniformity control, irreversibility and complex batch manufacturing process. The present invention has the advantages of reversibility, precise control and suitability for large-scale manufacturing, and can be better used for the measurement of radiation thermometers. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a structural schematic diagram of a local bottom-gate thermal sensor device of a semiconductor carbon nanotube material of the present invention;

[0021] Figure 2 It is a flow chart of the semiconducting carbon nanotube sorting process of the present invention. DETAILED DESCRIPTION

[0022] The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments.

[0023] The structure of the local bottom-gate thermal sensor device based on the semiconductor carbon nanotube material of the present invention is as follows Figure 1 As shown, 1 is the source electrode; 2 is the gate insulating layer; 3 is the substrate; 4 is the gate electrode; 5 is the drain electrode; and 6 is the carbon nanotube film.

[0024] Figure 1 The S, G, and D in the figure represent the source 1 (Source), the gate 4 (Gate), and the drain 5 (Drain) respectively.

[0025] The gate 4 is located at the bottom of the device, is composed of 10 nm thick titanium (Ti) and 50 nm thick palladium (Pd), and is isolated from the carbon nanotube film 6 by the gate insulating layer 2 .

[0026] The source electrode 1 and the drain electrode 5 are located at both ends of the carbon nanotube film, and are both composed of 10 nm thick titanium (Ti) and 50 nm thick palladium (Pd), forming a current path.

[0027] The channel length between the source and drain electrodes is designed to be 20 μm, and the electrode width is 100 μm.

[0028] The gate insulating layer 2 is made of HfO 2 Composition, thickness is 10nm.

[0029] The carbon nanotube film 6 is a mesh film composed of semiconductor single-walled carbon nanotubes, and has a thickness of about 4-10 nm.

[0030] The source electrode 1 , the gate electrode 4 , and the drain electrode 5 are all passed through by the central axis of the entire device and are symmetrically arranged about the central axis.

[0031] The central axis of the entire device refers to the central axis of the gate electrode 4 .

[0032] Reference Figure 2 , the process flow of sorting semiconductor carbon nanotubes of the present invention is further described in detail.

[0033] Step 1: 12 mg of semiconducting single-walled carbon nanotubes (SWCNTs) produced by an arc method and 12 mg of conjugated polymer poly[9-(1-octylnonyl)-9H-carbazole] (PCZ) are placed in a beaker and mixed with 50 ml of toluene.

[0034] Step 2, using an ultrasonic crusher to perform ultrasonic treatment for 30 minutes at an amplitude of 40%. During the ultrasonic dispersion process, the beaker is placed in an ice water bath for cooling, and a uniformly dispersed oily dispersion is obtained.

[0035] Step 3: Use an ultra-high speed centrifuge to pre-centrifuge at 4° C. and 20,000 g for 30 min to remove amorphous carbon, impurities and most of the m-SWCNTs, and collect 90% of the supernatant.

[0036] Step 4: Use an ultra-high speed centrifuge to perform secondary centrifugation at 4° C. and 50,000 g for 120 min to improve the purity of s-SWCNTs in the supernatant. 90% of the supernatant is a semiconductor single-walled carbon nanotube solution with a purity of up to 99%.

[0037] Reference Figure 2 , the local bottom gate structure of the device of the present invention is further described in detail.

[0038] The specific process of the present invention for making a local bottom-gate device based on a carbon nanotube network is as follows:

[0039] Step 1: Select a square silicon wafer with a side length of 2 cm as the substrate.

[0040] Step 2: grow a 10nm thick layer of hafnium oxide (HfO) on the surface of the silicon wafer by plasma enhanced chemical vapor deposition (PECVD) technology. 2 ) as the initial dielectric layer.

[0041] In step 3, a gate electrode region is patterned using a photomask, and 10 nm thick titanium (Ti) and 50 nm thick palladium (Pd) are sequentially deposited as a gate metal layer (Ti / Pd) by sputtering deposition technology.

[0042] Step 4: Grow a 10nm thick HfO layer on the gate metal layer again using PECVD technology. 2as a gate dielectric layer.

[0043] Step 5: Use a photomask to pattern the ohmic electrode region, and use the same sputtering deposition process to deposit a Ti / Pd metal layer (Ti 10nm / Pd 50nm) as the ohmic electrode.

[0044] Step 6: immerse the device in a pre-sorted semiconductor carbon nanotube solution by dip coating. After immersion for 48 hours, a uniform and dense carbon nanotube network film is formed on the surface of the device.

[0045] Step 7: Use a photomask to define the active area of ​​the device, protect the carbon nanotubes in the active area, and remove the carbon nanotubes between different devices by plasma etching technology to achieve electrical isolation of the devices.

[0046] Step 8: Use a photomask to define the gate opening area, and complete the preparation of the gate opening by a fluorine-based (F-based) etching process. After the above steps, a local bottom-gate device based on a carbon nanotube network is successfully prepared.

[0047] The specific process of using the local bottom gate architecture to control the resistance of the carbon nanotube film is as follows:

[0048] Step 1: On a temperature-controlled probe station, adjust the ambient temperature (0°C-50°C) and monitor the resistance change of the carbon nanotube sensor.

[0049] Step 2: Use Keithley 1505 to apply gate voltage and record the current-voltage characteristics of the device at different temperatures.

[0050] Step 3, by fitting the RT curve, calculate TCR = (1 / R) · (dR / dT), the result shows that when the gate voltage is +3V, TCR≈3%, and when the gate voltage is -3V, TCR≈-0.1%.

Claims

1. An uncooled infrared sensor based on a semiconductor carbon nanotube film, characterized in that: A semiconductor carbon nanotube film is used as the thermistor layer. The resistance of the thermistor film is regulated by adjusting the gate voltage through a local bottom-gate device structure, and different resistance temperature coefficients are exhibited under different gate voltages.

2. The uncooled infrared sensor according to claim 1, characterized in that: The local bottom-gate device structure comprises a source electrode, a gate insulating layer, a substrate, a gate electrode, a drain electrode, and a semiconductor carbon nanotube film which are arranged in sequence from bottom to top.

3. The uncooled infrared sensor according to claim 1, characterized in that: The channel length between the source and drain electrodes of the local bottom gate device is designed to be 20μm, the electrode width is 100μm, the gate insulation layer 2 is composed of HfO2 and has a thickness of 10nm, the source electrode, the gate electrode, and the drain electrode are all composed of 10nm thick titanium (Ti) and 50nm thick palladium (Pd) as metal layers (Ti / Pd), and the source electrode, the gate electrode, and the drain electrode are all passed through the central axis of the overall device and are symmetrically arranged about the central axis. The central axis of the overall device refers to the central axis of the gate electrode.

4. The uncooled infrared sensor according to claim 1, characterized in that: The semiconductor carbon nanotube film is sorted by using conjugated polymer materials.

5. The uncooled infrared sensor according to claim 4, characterized in that: The conjugated polymer material is poly[(9,9-dioctylfluorenyl-2,7-diyl)-alt(6,6′-{2,2′-bipyridine})](PFO-BPy), poly[(9,9-di-n-octylfluorenyl-2,7-diyl)-alt-(benzo[2,1,3]thiadiazole-4,8-diyl)](F8BT), poly(9,9-dioctyl-fluorenyl-2,7-diyl-pyridine-2,6-diyl))(PFP), (1-octanoyl)-9H-carbazole-2,7-diyl-alt-pyridine-2,6-diyl](PCP), poly(9,9-di-n-octylfluorenyl-2,7-diyl))(PFO), poly[9-(1-octylnonyl)-9H-carbazole] Any one of (PCZ).

6. The uncooled infrared sensor according to claim 2, characterized in that: The method of regulating the gate voltage to control the thermistor film resistance and showing different resistance temperature coefficients under different gate voltages means that the prepared uncooled infrared sensor is a p-type device, the device is turned on under a negative gate voltage, and the resistance is small; the device is turned off under a positive gate voltage, and the resistance is large; under different gate voltages, the device shows different resistance temperature coefficients; under a positive gate voltage, the resistance of the device increases with increasing temperature, and at a gate voltage of 3V, the resistance temperature coefficient is about 3%, which is equivalent to that of vanadium oxide, and the semiconductor carbon nanotube film can be used for the measurement of a radiation thermometer; under a negative gate voltage, the resistance of the device decreases with increasing temperature, and the resistance temperature coefficient is about -0.1% under a gate voltage of -3V.

7. A method for preparing an uncooled infrared sensor based on a semiconductor carbon nanotube film according to claim 1, characterized in that: The method includes sorting a semiconductor carbon nanotube film solution and generating a local bottom gate structure.

8. The preparation method according to claim 7, characterized in that: The steps of sorting the semiconductor carbon nanotube film solution are as follows: pre-centrifuging the dispersion for 30 minutes using a high-speed centrifuge, with an average centrifugal force of 20,000 g and a temperature controlled at 4° C. to remove most impurities and metal tubes in the solution; After the pre-centrifugation, 90% of the supernatant was collected and subjected to secondary centrifugation for 2 h. The average centrifugal force was set to 50,000 g and the temperature was controlled at 4° C. Finally, 90% of the supernatant was taken out as a semiconductor carbon nanotube solution to complete the solution sorting.

9. The preparation method according to claim 7, characterized in that: The steps of generating a local bottom gate structure are as follows: using a silicon wafer as a substrate, growing a 10nm thick hafnium oxide (HfO2) initial dielectric layer by plasma enhanced chemical vapor deposition (PECVD); defining a gate region by a photomask, and sputtering and depositing a titanium / palladium (Ti 10nm / Pd 50nm) metal layer; preparing a 10nm thick HfO2 gate dielectric layer on the gate by PECVD; defining an ohmic electrode region by a photomask, and repeatedly sputtering and depositing a Ti / Pd metal layer; forming a carbon nanotube network film on the device surface by a dip coating method; then achieving electrical isolation of the device by combining a photomask with plasma etching; completing gate opening by a photomask and fluorine-based etching, and finally obtaining a carbon nanotube network device with a local bottom gate structure.

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