Aln high temperature temperature sensor and method of making same

Abstract

The application discloses an AlN high-temperature temperature sensor and a manufacturing method, and mainly solves the problems of complex structure, easy interference and low test precision of the existing high-temperature temperature sensor. The AlN high-temperature temperature sensor comprises a substrate, an AlN film and an electrode. The substrate is made of any one of sapphire, silicon, silicon carbide, aluminum nitride or quartz; the electrode is made of high-temperature resistant materials such as Pt / Rh, Ti / Au, Ni / Au or Pd / Au, and adopts a finger electrode structure; the AlN film is located between the substrate and the metal electrode, and forms a three-layer vertical structure to obtain a temperature-related electrical signal. In operation, the AlN film on the substrate is intrinsically excited to be enhanced at high temperature, the number of carriers and the resistivity change regularly, the electrode collects and outputs the temperature-related electrical signal, and the electrical characterization of temperature is realized. The AlN high-temperature temperature sensor has the advantages of strong anti-interference ability, simple structure, easy integrated manufacturing, simple signal reading, high temperature measurement precision and the like, and can be used for 500-900 DEG C high-temperature temperature sensing large-scale integrated circuits.

Description

Technical Field

[0001] This invention belongs to the field of microelectronic device technology, and specifically relates to an AlN high-temperature temperature sensor that can be used in ultra-large-scale integrated circuits for high-temperature sensing at 500-900℃. Background Technology

[0002] A temperature sensor is a device or apparatus that can sense the temperature of an object and convert this non-electrical physical quantity into a measurable and transmittable electrical signal. It is a core component for realizing temperature detection, acquisition, and automatic control. Currently, the main materials for temperature sensors are silicon-based resistors and PN junctions, with an upper operating temperature limit of around 300℃. Sensors with higher temperatures are mainly thermocouple structures, but their disadvantage is that they are not easy to integrate with chips into integrated circuits; there are no high-temperature temperature sensors that can be integrated with chips.

[0003] Patent document CN202110255505.2 discloses a piezoelectric thin-film temperature sensor and its fabrication method. The sensor uses a substrate as a base, with the following layers stacked from bottom to top: a Bragg reflector layer is integrally deposited on the substrate; a first electrode is fabricated in a localized area of ​​the Bragg reflector layer facing away from the substrate, and the remaining area and the surface of the first electrode are covered by a single-crystal piezoelectric thin-film layer; a second electrode is completely disposed on the outer surface of the piezoelectric thin-film layer facing away from the first electrode. Because this sensor employs an FBAR (Bulk Acoustic Resonator) thin-film structure, its structure is complex, and the stress, vibration, and pressure it experiences are easily coupled with the temperature signal, leading to inaccurate measurements.

[0004] Patent document CN202310224959.2 discloses an AlN thin film temperature sensor and temperature measurement method for aero-engine turbine blades. It uses an AlN piezoelectric coating, which is applied to the object under test. The temperature is accurately characterized by measuring at least one of the following: surface cross-sectional morphology, grain size, grain structure, diffraction peak intensity and full width at half maximum (FWHM), and elemental composition of the AlN piezoelectric coating. However, the actual application of this device is cumbersome, resulting in low testing accuracy.

[0005] In summary, existing piezoelectric thin-film temperature sensors employ an FBAR (Bulk Acoustic Resonator) structure, which is susceptible to interference from stress, vibration, and pressure. Existing AlN thin-film temperature sensors for aero-engine turbine blades use an AlN piezoelectric coating applied to the object under test, requiring characterization of the measured temperature through surface cross-sectional morphology, grain size, and elemental composition, resulting in low testing accuracy. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of the prior art by providing an AlN high-temperature temperature sensor and its manufacturing method, thereby simplifying the temperature sensor structure, avoiding interference from stress, vibration, and pressure, and improving temperature measurement accuracy.

[0007] The technical approach to achieving the objective of this invention is as follows: by using a vertical three-layer structure of "substrate-AlN-electrode", the device structure is made simpler and is not affected by stress, vibration, or pressure; by utilizing the thermistor properties of AlN, electrical signals are directly used to characterize the test temperature, thereby improving the test accuracy.

[0008] Based on the above ideas, the technical solution of the present invention includes:

[0009] 1. An AlN high-temperature temperature sensor, comprising a substrate, an AlN thin film, and electrodes, characterized in that,

[0010] The electrodes are interdigitated electrodes to obtain more accurate temperature measurement data;

[0011] The AlN thin film, located above the substrate and below the metal electrode, forms a three-layer vertical structure to obtain temperature-dependent electrical signals.

[0012] Furthermore, the substrate may be any one of sapphire, silicon, silicon carbide, aluminum nitride, or quartz.

[0013] Furthermore, the electrode has a thickness of (1-10000) nm and uses high-temperature resistant materials such as Pt / Rh, Ti / Au, Ni / Au, TiW / Au, or Pd / Au to achieve device stability at high temperatures.

[0014] Furthermore, the AlN film has a thickness of (1-100000) nm and is used for temperature detection.

[0015] 2. A method for fabricating an AlN high-temperature temperature sensor, characterized in that it includes:

[0016] S1) Select a substrate and perform pretreatment such as polishing, cleaning and drying on it;

[0017] S2) An AlN thin film is epitaxially grown on the surface of a pretreated substrate by physical vapor deposition or chemical vapor deposition for temperature sensing.

[0018] S3) The AlN film is cleaned and dried;

[0019] S4) Pt / Rh, Ti / Au, or Ni / Au high-temperature electrodes are prepared on the cleaned and dried AlN thin film by magnetron sputtering, electron beam evaporation, or photolithography and lift-off processes to detect current signals and complete the sensor fabrication.

[0020] Compared with the prior art, the present invention has the following advantages:

[0021] 1. Strong anti-interference ability and high temperature measurement accuracy:

[0022] Existing FBAR sensors, based on changes in acoustic resonant frequency, are highly susceptible to coupling interference from external stress, vibration, and pressure, leading to measurement errors. This invention, however, utilizes the intrinsic thermistor properties of AlN material to characterize temperature by measuring current or resistance. This electrical parameter primarily depends on the carrier concentration and mobility within the material and is insensitive to external mechanical stress, vibration, and pressure. Therefore, this invention fundamentally avoids mechanical interference, significantly improving the accuracy and reliability of temperature measurement under complex operating conditions.

[0023] 2. Simple structure, easy to integrate and low-cost to manufacture.

[0024] This invention employs a simple three-layer vertical structure of "substrate-sensitive layer-electrode," eliminating the need for complex resonant cavity structures or additional signal compensation circuits. Therefore, the process flow is simpler, yields higher output, and costs lower. Furthermore, the planar structural design makes it more compatible with existing semiconductor integrated circuit processes, facilitating monolithic integration of sensors and control chips. This fills the technological gap in achieving high-precision, interference-resistant temperature sensing and monolithic integration of AlN materials under extreme high-temperature environments.

[0025] 3. Signal reading is simple and requires no complex characterization.

[0026] Unlike existing technologies that rely on analyzing surface morphology, grain size, and elemental composition to indirectly infer temperature, this invention can directly output a standard electrical signal. This means that real-time, online temperature monitoring can be achieved using only conventional readout circuits, greatly simplifying the testing system and data processing flow, and meeting the requirements of real-time performance and convenience in industrial settings. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the structure of the AlN high-temperature temperature sensor of the present invention;

[0028] Figure 2 This is a process flow diagram of the AlN high-temperature temperature sensor of the present invention.

[0029] Figure 3 This is a curve showing the change of current with temperature at -100V for the AlN thermistor of this invention. Detailed Implementation

[0030] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention and not all embodiments. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative effort should all fall within the protection scope of the present invention.

[0031] It should be noted that the step numbers in the specification and claims of this invention are only for the purpose of clearly describing the embodiments of this invention and facilitating understanding, and their order is not limited.

[0032] Reference Figure 1 The AlN high-temperature temperature sensor of the present invention includes: a substrate, a sensitive layer, and an electrode, wherein...

[0033] The substrate may be any one of sapphire, silicon, silicon carbide, aluminum nitride, or quartz.

[0034] The sensitive layer, located on the upper surface of the substrate, is an AlN thin film with a thickness of (1-100000) nm, used for temperature detection.

[0035] The electrode is an interdigitated electrode with a finger width of (1-1000) μm, a finger spacing of (1-1000) μm, a finger length of (1-2000) μm, a total thickness of (1-10000) nm, and a finger pair number of (1-100) pairs. It includes a positive electrode and a negative electrode, which are located on both sides of the upper surface of the sensitive layer, forming a vertical three-layer structure with the substrate and the sensitive layer. It uses any one of the high-temperature resistant materials Pt / Rh, Ti / Au, Ni / Au, TiW / Au, or Pd / Au to achieve device stability at high temperatures.

[0036] The working principle of this device is based on the thermistor characteristics of AlN thin film in a high-temperature environment of (500-900)℃. That is, at high temperature, the intrinsic excitation of AlN thin film on the substrate is enhanced, and the number of charge carriers changes regularly with temperature, which is reflected in the regular change of resistivity. Temperature-related electrical signals are collected and output through interdigital electrodes, thereby realizing the electrical characterization of temperature.

[0037] Reference Figure 2 The present invention provides the following three embodiments:

[0038] Example 1: Fabrication of an AlN sensor based on a sapphire substrate and Pt / Rh electrodes.

[0039] Step 1: Substrate pretreatment.

[0040] 1.1) Select c-plane sapphire as the substrate;

[0041] 1.2) The substrate was polished under the following conditions: polishing abrasive particle size of 0.8 micrometers, polishing pressure of 2 pounds per square inch, polishing speed of 45 rpm, and polishing time of 20 minutes. This polishing step can make the substrate surface smoother and reduce surface roughness, providing good interface conditions for the subsequent growth of AlN thin films, and helping to improve the quality and performance of AlN thin films.

[0042] 1.3) The polished sapphire substrate is placed in a mixture of sulfuric acid and hydrogen peroxide in a volume ratio of 3:1 and cleaned at 120°C for 15 minutes to effectively remove organic impurities and some metallic impurities from the substrate surface and further clean the substrate surface.

[0043] 1.4) Rinse the substrate thoroughly with deionized water to ensure that the residue of the mixture is completely removed. During multiple rinsing processes, each rinse should last no less than 5 minutes, and the deionized water should be changed at least 3 times to ensure the cleaning effect.

[0044] 1.5) Place the substrate in an oven at 120°C and bake for 20 minutes to dry it, ensuring that there are no water stains on the substrate surface, thus providing a good foundation for the subsequent growth of AlN thin films.

[0045] Step 2: Epitaxial growth of AlN thin film.

[0046] An AlN thin film with a thickness of approximately 500 nm was grown on a pretreated sapphire substrate using reactive magnetron sputtering. The process parameters were set as follows: a high-purity aluminum target (99.99% purity), a target-to-substrate distance of 5 cm, an Ar / N2 flow rate ratio of 1:2 (Ar flow rate 15 sccm, N2 flow rate 30 sccm), a deposition pressure of 1.0 Pa, an RF power of 200 W, a substrate temperature of 200 °C, and a deposition time of 2 hours.

[0047] Step 3: Cleaning and drying of AlN film.

[0048] The grown AlN film samples were placed in acetone, alcohol, and ultrapure water in sequence, and each was cleaned for 15 minutes using an ultrasonic cleaner at 25°C. Finally, they were dried with nitrogen gas.

[0049] Step 4: Prepare Pt / Rh interdigitated electrodes.

[0050] A Pt / Rh rectangular electrode with a total thickness of approximately 300 nm, a width of 10 μm, a length of 500 μm, and a mass ratio of 90:10 was fabricated on an AlN thin film using magnetron sputtering. The process parameters were: Ar gas flow rate of 30 sccm, sputtering gas pressure of 1.0 Pa, sputtering power of 150 W, substrate temperature of 300 °C, and deposition time of 20 minutes. The device fabrication was then completed.

[0051] Example 2: Fabrication of an AlN sensor based on a silicon substrate and Ti / Au electrodes.

[0052] Step 1: Substrate pretreatment.

[0053] P-type (100) monocrystalline silicon was selected as the substrate, and the polishing parameters were set as follows: a polishing abrasive particle size of 0.5 micrometers, a polishing pressure of 1 psi, and a polishing speed of 10 rpm. The substrate was first polished for 30 minutes to remove the damaged layer caused by cutting, reduce surface defects, and improve surface flatness, providing a good foundation for the subsequent growth of high-quality AlN films. Next, the substrate was cleaned using the standard RCA process. First, it was cleaned with SC-1 solution (NH4OH:H2O2:H2O = 1:1:5, 75℃) for 10 minutes to remove organic impurities and some metal impurities from the substrate surface. Then, it was cleaned with SC-2 solution (HCl:H2O2:H2O = 1:1:6, 75℃) for 10 minutes to further remove metal impurities. After that, it was rinsed thoroughly with deionized water to completely remove the cleaning solution residue. Finally, the substrate was placed in an oven at 100℃ for 30 minutes to dry it, ensuring that there were no water stains on the substrate surface.

[0054] Step 2: Epitaxial growth of AlN thin film.

[0055] With the following process conditions set: aluminum source as trimethylaluminum at a flow rate of 5 sccm; nitrogen source as ammonia at a flow rate of 500 sccm; carrier gas as high-purity hydrogen at a flow rate of 2 slm; reaction pressure of 10 torr; substrate temperature of 800℃; and growth time of 0.5 hours, an AlN thin film with a thickness of approximately 10 nm was grown on a pretreated silicon substrate using metal-organic chemical vapor deposition.

[0056] Step 3: Cleaning and drying of the AlN film.

[0057] The grown AlN film samples were placed in acetone, alcohol, and ultrapure water in sequence, and cleaned for 10 minutes each using an ultrasonic cleaner at 20°C. Finally, they were dried with nitrogen gas.

[0058] Step 4: Prepare Ti / Au interdigitated electrodes.

[0059] Ti / Au interdigitated electrodes with a finger width of 5 μm, a finger spacing of 5 μm, a finger length of 300 μm, and 15 interdigitated finger pairs were fabricated on AlN thin films using photolithography and lift-off processes. The specific steps are as follows:

[0060] First, the spin coating speed was set to 2000 rpm and the spin coating time was 30 seconds. AZ5214 photoresist with a thickness of about 1 μm was spin-coated on the AlN film surface. The photoresist was then pre-baked on a 90℃ hot plate for 90 seconds. After cooling, it was exposed for 1 second using an interdigitated electrode mask. Then, it was reverse-baked on a 110℃ hot plate for 60 seconds. After general exposure for 20 seconds, it was developed with AZ400K developer for 30 seconds. It was then rinsed with deionized water and dried with nitrogen.

[0061] Then, with the process parameters set to an evaporation rate of 0.1 Å / s and a substrate temperature of 20 °C, an electron beam evaporation process was used to deposit a Ti adhesion layer with a thickness of approximately 20 nm.

[0062] Next, with the process parameters set to an evaporation rate of 2 Å / s and a substrate temperature of 20 °C, an Au conductive layer with a thickness of approximately 200 nm was deposited on the adhesion layer using an electron beam evaporation process.

[0063] Finally, the sample is placed in acetone for stripping to remove the photoresist and excess metal layer, resulting in patterned Ti / Au interdigitated electrodes, thus completing the device fabrication.

[0064] Example 3: Fabrication of an AlN sensor based on a silicon carbide substrate and Ni / Au electrodes.

[0065] Step A: Select silicon carbide as the substrate and pretreat it.

[0066] A1) The substrate is first polished for 10 minutes under the process parameters of polishing abrasive particle size of 1 micrometer, polishing pressure of 3 pounds / square inch and polishing speed of 60 rpm;

[0067] A2) The polished substrate is cleaned using the standard RCA process, which involves first cleaning it in SC-1 solution at 75°C for 12 minutes, and then cleaning it in SC-2 solution at the same temperature for 12 minutes to remove impurities from the substrate surface. The substrate is then rinsed thoroughly with deionized water to avoid cleaning solution residue.

[0068] A3) Place the cleaned substrate in an oven at 140°C and bake for 30 minutes to dry it.

[0069] Step B: Epitaxial growth of AlN thin film.

[0070] B1) Under the following process conditions: the target material is a high-purity aluminum target, the distance between the target and the substrate is 6 cm, the Ar / N2 flow ratio is 1:3 (Ar flow rate 10 sccm, N2 flow rate 30 sccm), the deposition pressure is 2 Pa, the RF power is 300 W, the substrate temperature is 350 °C, and the deposition time is 3 hours, an AlN thin film with a thickness of approximately 100,000 nm is grown on a pretreated silicon carbide substrate using reactive magnetron sputtering.

[0071] B2) Place the grown AlN film sample in acetone, alcohol and ultrapure water in sequence, and clean each sample for 20 minutes in an ultrasonic cleaner at 30°C. Finally, dry the sample with nitrogen gas.

[0072] Step C: Prepare Ni / Au interdigitated electrodes.

[0073] C1) Under the process conditions of evaporation rate of 0.3 Å / s and substrate temperature of 300 °C, an Ni adhesion layer with a thickness of about 20 nm was deposited on AlN film using electron beam evaporation.

[0074] C2) An 80 nm Au conductive layer is deposited on the adhesion layer using an electron beam evaporation process under the conditions of an evaporation rate of 0.5 Å / s and a substrate temperature of 300 °C.

[0075] C3) Photoresist is spin-coated onto the surface of a Ni / Au double metal film. After pre-baking, exposure is performed using a mask. After development, an interdigitated electrode protection pattern with a finger width of 3μm, a finger spacing of 3μm, a finger length of 200μm, and 20 pairs of interdigitated fingers is obtained.

[0076] C4) Ion beam etching removes metal areas not protected by photoresist;

[0077] C5) Remove the remaining photoresist and process it through a standard cleaning process to finally obtain the required Ni / Au interdigitated electrodes and complete the device fabrication.

[0078] The effects of this invention can be further illustrated by the following test results:

[0079] I. Test Conditions:

[0080] The testing equipment uses a high-temperature probe station, a digital source meter, and a temperature controller; the test temperature range is (500-900)℃, the test step is 50℃, the heating rate is 15℃ / minute, and the applied voltage is -100V.

[0081] II. Test Content:

[0082] Under the above test conditions, the current-temperature characteristics of the temperature sensor of Embodiment 1 of the present invention were tested, namely...

[0083] Within the temperature range of 500℃-900℃, the current value of the sensor at -100V was measured every 50℃, and a curve of current versus temperature was plotted. The results are as follows. Figure 3 As shown.

[0084] from Figure 3 As can be seen, the current of this device changes regularly with temperature, indicating that it can be used as a high-performance high-temperature sensor.

[0085] The above descriptions are merely three specific examples of the present invention and do not constitute any limitation on the present invention. Obviously, those skilled in the art, after understanding the content and principles of the present invention, may make various modifications and changes in form and detail without departing from the principles and structure of the present invention, including:

[0086] In addition to the sapphire, silicon, and silicon carbide substrates used in the three examples above, other high-temperature resistant and insulating materials such as aluminum nitride or quartz can also be used as substrates. Different substrate materials may have different physical properties such as thermal expansion coefficients and lattice constants. Selecting a suitable substrate may further optimize the performance of the sensor.

[0087] In addition to the high-temperature resistant electrode materials Pt / Rh, Ti / Au, and Ni / Au used in the three examples above, other alloy materials with high conductivity, high temperature resistance, and chemical stability, such as TiW / Au or Pd / Au, can also be used as electrodes.

[0088] In addition to the interdigitated electrode pattern used in the three examples above, the electrode pattern can also use rectangular electrodes or other complex patterns, such as spiral electrodes or honeycomb electrodes. Different electrode patterns will affect the electric field distribution and current transmission path of the sensor, thereby affecting the accuracy and sensitivity of the temperature measurement data.

[0089] In addition to the process flow used in the three examples above, the fabrication method can add some process steps to further optimize the sensor performance based on the existing process flow. For example, after growing the AlN thin film, a high-temperature annealing treatment can be performed to eliminate stress and defects in the film and improve the crystal quality of the film.

[0090] However, the modifications and alterations based on the ideas of this invention are still within the scope of protection of the claims of this invention.

Claims

1. An AlN high-temperature temperature sensor, comprising a substrate, an AlN thin film, and electrodes, characterized in that, The electrodes are interdigitated electrodes to obtain more accurate temperature measurement data; The AlN thin film, located above the substrate and below the metal electrode, forms a three-layer vertical structure to obtain temperature-dependent electrical signals.

2. The sensor according to claim 1, characterized in that, The substrate may be any one of sapphire, silicon, silicon carbide, aluminum nitride, or quartz.

3. The sensor according to claim 1, characterized in that, The electrode has a thickness of (1-10000) nm and uses high-temperature resistant materials such as Pt / Rh, Ti / Au, Ni / Au, TiW / Au, or Pd / Au to achieve device stability at high temperatures.

4. The sensor according to claim 1, characterized in that, The AlN film has a thickness of (1-100000) nm and is used for temperature detection.

5. A method for fabricating an AlN high-temperature temperature sensor, characterized in that, include: S1) Select a substrate and perform pretreatment such as polishing, cleaning and drying on it; S2) An AlN thin film is epitaxially grown on the surface of a pretreated substrate by physical vapor deposition or chemical vapor deposition for temperature sensing. S3) The AlN film is cleaned and dried; S4) High-temperature resistant electrodes of Pt / Rh, Ti / Au, Ni / Au, TiW / Au, or Pd / Au are prepared on the cleaned and dried AlN film by magnetron sputtering, electron beam evaporation, or photolithography and lift-off processes for detecting current signals, thus completing the sensor fabrication.

6. The method according to claim 5, characterized in that, The pretreatment of polishing, cleaning and drying the substrate in S1) is implemented as follows: Polishing process parameter settings: polishing abrasive particle size is (0.5-1) micrometers, polishing pressure is (1-3) pounds / square inch, polishing speed is (10-60) revolutions / minute, and polishing time is (10-30) minutes; For silicon and silicon carbide substrates, the standard RCA process is used for cleaning; for sapphire substrates, sulfuric acid and hydrogen peroxide are used for cleaning. Drying process: Dry with nitrogen or bake in an oven at (100-140)℃ for (10-30) minutes.

7. The method according to claim 5, characterized in that, In step S2), AlN thin films are grown by physical vapor deposition or chemical vapor deposition, and the process conditions are as follows: Physical vapor deposition parameter settings: The target material is an aluminum target with a purity of 99.99%. The distance between the target and the substrate is (1-6) cm. Ar / N2 flow ratio (1:1-1:3). Deposition gas pressure (0.5-2) Pa, RF power (100-300) W, Deposition time (0.1-3) hours; Chemical vapor deposition parameter settings: The aluminum source is trimethylaluminum (TMA), and the nitrogen source is ammonia (NH3). TMA flow rate (5-200) sccm, NH3 flow rate (500-5000) sccm Carrier gas flow rate (2-20) slm, Reaction pressure (10-200) torr, Substrate temperature (800-1200)℃, Growth time (0.5-4) hours.

8. The method according to claim 5, characterized in that: The cleaning process in S3) is to use acetone, alcohol and ultrapure water sequentially in an ultrasonic cleaner for 10-20 minutes at an ambient temperature of (20-30)℃. The drying process described in S3) involves drying with nitrogen or baking in an oven at (100-120)°C for (10-30) minutes.

9. The method according to claim 5, characterized in that, In step S4), Pt / Rh, Ti / Au, or Ni / Au high-temperature resistant electrodes are prepared by magnetron sputtering, electron beam evaporation, or photolithography and lift-off processes, with the following process conditions: The parameter settings for the magnetron sputtering process are as follows: Ar gas flow rate (20-50) sccm, Sputtering pressure (0.5-2) Pa, Sputtering power (100-200) W, Substrate temperature (20-400)℃, Deposition time (1-300) minutes, Total electrode thickness (1-1000) nanometers; The electron beam evaporation process parameters are set as follows: Electron beam current (1-50) mA, Evaporation rate (0.1-2) Å / s, substrate temperature (20-300) °C, Evaporation time (1-30) minutes; The photolithography parameters are set as follows: The photoresist used is from the AZ series. Spin coating speed (2000-5000) rpm Time (10-200) seconds, The photoresist thickness is (0.1-3) micrometers. Pre-drying temperature (90-110)℃, Exposure time (1-60) seconds, Developing time (10-200) seconds.

10. The method according to claim 5, characterized in that, The patterned electrodes in S4) include interdigitated electrodes, rectangular electrodes, or other complex patterns.

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