Robust wide dynamic range interferometric microthermometer and method of manufacture

Abstract

The present invention relates to a robust wide dynamic range interferometric microthermometer and method of manufacture. Thermometry based on optical transduction mechanisms provides advantages over other thermometry techniques; however, there are certain challenges related to reproducibility and reliability that have hindered its general use until now. The present invention discloses a Ga2O3:Cr nanowire- or microwire-based microthermometer, characterised in that the entire structure is coated with a sheet made up of an Al2O3 layer or another low refractive index material and with a DBR nanometric structure formed by two transparent oxides. The microthermometer measures temperature in a simple way by using a luminescent and interferometric dual-transduction mechanism that is robust, accurate and reliable and that can operate in a wide range of temperatures and under adverse conditions. It can be integrated into a microdevice as its method of manufacture produces a robust structure on a conventional bulk substrate such as silicon.

Description

[0001]

[0002] Robust wide dynamic range interferometric microthermometer and manufacturing method.

[0003] TECHNICAL SECTOR

[0004] The present invention relates to the manufacture and operation of a system for remote temperature measurement. More specifically, it relates to a microthermometer based on optical interference phenomena, applicable in fields such as healthcare, electronic devices, the aerospace sector, and the environment.

[0005] BACKGROUND OF THE INVENTION

[0006] The search for accurate and non-invasive methods for temperature measurement is an ongoing challenge in scientific exploration and technological progress, as temperature monitoring is a key aspect of numerous fields ranging from healthcare (e.g., cancer cell monitoring and treatment) to electronic devices (particularly due to heat issues related to miniaturization, which can lead to failures, including electronics in the aerospace industry, where devices made of highly stable and radiation-resistant materials are required) to environmental studies, where highly stable and weather-resistant devices are highly beneficial.

[0007] Among the wide variety of techniques currently available for this purpose, thermometry based on optical transduction mechanisms has emerged as a promising and versatile approach, as it offers advantages over other thermometric techniques, such as its ability to provide highly accurate temperature measurements without physical contact. Therefore, it is ideal for applications in extreme environments, in addition to the potential it offers for use in micro- and nanometer-scale systems due to the small size of the luminescent temperature sensor. Among optical thermometry techniques, luminescent thermometry allows temperature measurement at the nanometer level, measuring only luminescent intensity. A wide variety of techniques exist for this purpose, depending on the materials, mechanisms, operating ranges, and resolution or sensitivity. Depending on the application requirements (temperature resolution, temperature range, environment, etc.),) certain thermometers will be more suitable than others. For example, for in vivo applications, biocompatibility, precision, and high reliability are required. Therefore, UCNPs (upconverting nanoparticles with a diameter of 1 to 100 nm and exhibiting photon upconversion) and QDs (quantum dots or structures synthetically created in laboratory settings, designed to trap electrons in incredibly small spaces) are the most widely used nanomaterials as luminescent thermometers in this sector. However, these thermometers typically operate within a narrow temperature range, which is sufficient for biological or biomedical applications, but this is not the case for industrial and environmental applications where typical operating temperatures reach several hundred °C. Although luminescent thermometers that can operate within wide temperature ranges have been described (Debasu, Mengistie L, et al.All-in- one optical heater-thermometer nanoplatform operative from 300 to 2000 K based on Er. 3 * emission and blackbody radiation. Advanced Materials 25.35 (2013): 4868-4874; Marciniak, L, et al. Optimization of highly sensitive YAG: Or 3 *, Nd 3+ nanocrystal-based luminescent thermometer operating in an optical window of biological tissues, Physical Chemistry Chemical Physics 19.10 (2017): 7343-7351 ; Elzbieciak-Piecka, Karolina, et al. C / J+ based nanocrystalline luminescent thermometers operating in a temporal domain, Physical Chemistry Chemical Physics 22.44 (2020): 25949-25962), por Io general, aún existen ciertos obstáculos relacionados con la reproducibilidad y la fiabilidad que han impedido su uso generalizado (Bradac, C., et al. Optical nanoscale thermometry: from fundamental mechanisms to emerging practical applications, Advanced Optical Materials 8.15 (2020): 2000183).

[0008] Another optical thermometry technique is based on exploiting optical interference phenomena, where the interaction of two or more light waves produces a resultant intensity that deviates from the simple sum of the individual intensities. An important advantage of interferometric thermometers is that the dependence of the physical parameter of the medium (wavelength shift, related to the light interference conditions) on temperature follows a linear (Feng, Jing, et al. An optical fiber tip micrograting thermometer, IEEE Photonics Journal 3.5 (2011): 810–814) or quadratic relationship over a wide temperature range. This improves the ease of calibration and has the potential to extend the dynamic temperature range.However, the challenge for interferometric devices based on optical cavities made of material systems with suitable morphologies, such as variable rectangular section fibers, is to optimize the quality of the optical resonances, since the position of the resonance maxima is the variable parameter with temperature that gives the reading of the same.

[0009] For all the above reasons, a robust and reliable micrometric temperature measurement system would be desirable, operating over a wide temperature range (from cryogenic to several hundred degrees Celsius), while still being able to obtain a local temperature reading in a remote environment, i.e., at a certain distance from the environment with which the probe is in contact.

[0010] To this end, a single platform would be ideal that provides a simple dual transduction mechanism for temperature measurement; that is, one that integrates two independent optical properties measurable as a function of temperature, such as luminescence mechanisms and an interferometric signal. This would allow for the development of more precise thermometers that can operate over a wide temperature range. A luminescent and interferometric microthermometer has recently been fabricated and tested (Alonso-Orts, Manuel, et al. Modal Analysis of fi-GaiC^Cr Widely Tunable Luminescent Optical Microcavities, Physical Review Applied 9.6 (2018): 064004). This thermometer is based on chromium-doped gallium oxide Ga2O3, where the material exhibits a red luminescence characteristic of Cr, and spatial patterns are created in the Ga2Oa nano- and microwires to operate as optical cavities.This thermometer allows easy quantification of interference-based peak shifts and operates over a wide temperature range (from -173°C to 277°C) with a thermal resolution of around 1°C. However, it has the disadvantage of a complex manufacturing process requiring great precision since these cavities are based on distributed Bragg reflectors (DBRs) fabricated by local, one-by-one etching using the Focused Ion Beam (FIB) technique to achieve the appropriate periodic hole patterns in the nano- and microwires that form the DBR mirrors and confine the light in the cavities. Furthermore, its quality is limited by the scatering of =20% of the incident light on the DBRs.On the other hand, nano- and microwires are placed on ultra-thin carbon networks in transmission electron microscope (TEM) grids, without contact with substrates, which makes implementation in microdevices or in extreme environments difficult and can easily lead to device breakage.

[0011] The present invention presents a microthermometer that measures temperature in a simple manner using a robust, precise, and reliable dual-transduction mechanism, both luminescent and interferometric. It can operate over a wide temperature range and under adverse conditions, such as high laser power or in liquids. It can also be integrated into a microdevice, since its manufacturing method allows for a robust structure. This new microthermometer is based on the one described above, but mitigates the complexity and fragility of the design. To achieve this, it protects the nano- and microwires that operate as optical cavities by encapsulating them in DBRs obtained by superimposing alternating layers of two materials.

[0012] There are systems with different applications where Bragg reflectors are protected inside structures. For example, document US6150190A describes the manufacture of a semiconductor device for reflecting electromagnetic radiation, comprising a Bragg reflector buried in a semiconductor substrate. Document US2014321502A1 describes a thermometer comprising a Bragg grating, which is a type of DBR constructed as a short segment within an optical fiber.

[0013] In the present invention, the DBRs protect the wire in which the optical resonances are generated. In addition, a trench is generated on each side or end of the nano- and microwires to optimize the behavior of the DBRs in this critical area of ​​the device and also facilitate the detection of light confined in the cavity. The technique employed allows the fabrication of more than one microcavity with identical DBRs on the same substrate, which facilitates the manufacturing process. Furthermore, the manufactured system can withstand intense radiation from lasers and other sources, making the microthermometer attractive for applications such as aerospace. Finally, the DBR grown on the wire prevents the microcavity from detaching from the substrate or breaking due to physical contact.Furthermore, it allows the cavity to function perfectly inside liquids such as ethanol or acetone, indicating its potential use in in vitro conditions or in temperature measurements involving liquid-solid interfaces.

[0014] EXPLANATION OF THE INVENTION

[0015] The present invention presents a luminescent and interferometric microthermometer and its manufacturing process. The microthermometer provides a robust and reliable temperature measurement system that operates over a wide temperature range, from cryogenic temperatures to several hundred degrees Celsius. The device can operate under adverse conditions, such as high power or radiation, or in liquids, making it suitable for use in various industrial and environmental applications, as well as in biological or biomedical applications.

[0016] The design of the luminescent interferometric microthermometer is based on Ga2Ü3:Cr nano- or microwires delimited by a trench on both sides of the elongated microstructure (nano- or microwire) made with a focused ion beam (FIB) and the conformal deposition of alternating oxide layers with a specific thickness around all facets of the nanowire or microwire. The design and methodology presented would be viable for any elongated microstructure that shows strong emission over a wide range of wavelengths.

[0017] More specifically, the luminescent and interferometric microthermometer based on Ga2Oa:Cr nanowires or microwires comprises: a) A layer of massive substrate. b) A layer deposited on the massive substrate, of nanometric thickness, with a structure of Bragg reflectors (DBR) of n periods (n being an integer or half-integer), and composed of two materials transparent to the light to be confined, but whose combination in the aforementioned DBR behaves as an efficient reflector of said light. c) A sheet deposited on layer b) and composed of a low refractive index material that allows the light emitted by the Ga2O3:Cr nanowires or microwires to be guided. d) Ga2O3:Cr nanowires or microwires deposited on the thick film c) which, when excited, for example, with a laser beam with a wavelength of 325 nm or 442 nm, emit light in the red-near infrared range, in the range between about 600 nm and 900 nm.e) A new layer c) deposited on the nanowires or microwires d) and which is parallel to each of its surfaces, both the upper and the lateral ones, defined by the three axes x, y, z. f) A new layer of DBR b) deposited on the layer e), which is also parallel to each of the surfaces of the nanowires or microwires, defined by the three axes x, y, z, including those of the final ends.

[0018] The manufacturing method for the luminescent and interferometric microthermometer combines the production of nanowires or microwires and the ALD (Atomic Layer Deposition) technique, or any other related deposition technique, as well as the FIB etching technique, to manufacture Bragg reflector structures (DBR) that encapsulate the nano- or microwires to form optical microcavities. More specifically, the manufacturing method comprises the following steps:

[0019] / . Obtaining Ga2O3:Cr nanowires or microwires as elongated structures that form the optical cavity.

[0020] / / . Fabrication of the DBR substrate using the ALD technique on a bulk substrate. This substrate, in turn, comprises: a) An n-period DBR made of AI2O3-T¡O2 with nanometric thicknesses. b) A thicker sheet of low refractive index material, such as AI2O3, over the structure indicated in step ii) a), essential for guiding the light emitted by the Ga2O3:Cr. iii. Deposition of the elongated structures obtained in step / onto the DBR substrate obtained in step (ii). iv.Making trenches perpendicular to the length of the nanowire or microwire (this direction defined by the length is parallel to the z-axis) using the FIB technique at the ends of the structures deposited in step (iii) such that the DBRs are parallel to each end surface of the deposited nanowires or microwires (if the trench is not made, it would be deposited on top of the DBR substrate created in step ii) and would gradually hinder the correct coating of the surfaces of the ends of the nano- or microwires with the DBRs). Specifically, the surface of the ends of the nanowire or microwire, as well as the surface of the DBRs at that end, is parallel to the XY plane. v. Depositing a low refractive index material plus an n-period DBR, equivalent to step i) but reversing the order of a) and b), on the top and lateral surroundings of the structure obtained in step (iv).

[0021] Elongated structures (nanowires or microwires) of Ga2O3:Cr can be synthesized (step i) by different appropriate techniques and should show strong emission over a wide range of wavelengths for a wide range of temperatures. An appropriate fabrication technique would be, for example, thermal evaporation using powders of gallium metal and chromium oxide (C^Ch) as precursors (Alonso-Orts, Manuel, et al. Wide dynamic range thermometer based on luminescent optical cavities in Ga2O3:Cr Nanowires, Small 18.1 (2022): 2105355.). Another fabrication method that results in elongated microstructures with strong emission and some waveguiding before patterning and that can be dispersed on a substrate, such as Molecular Beam Epitaxy (MBE), is also possible.

[0022] The DBR substrate obtained in step ii) is fabricated on a suitable bulk substrate, such as silicon, with dimensions, for example, of 0.5 x 0.5 cm z. The Al2O3-TIÜ2 DBR has, for example, four periods (n=4) and thicknesses of, for example, 113 nm for the Al2O3 layers and 75 nm for the TIÜ2 layers. These thicknesses are optimal for high reflectivity, around 70-80% of normal incident light in the Ga2O3:Cr emission range (670 - 780 nm), but other thicknesses that are optimal for other optically active materials in another wavelength range could be used instead. A higher number of periods increases the confinement of light in the optical cavity, but would require deeper and wider trenches to be made at the ends of the cavity in stage 3. The precursors used for the deposition of Al2O3 and TiO2 layers by ALD can be, for example, thiomethylaluminum / water and tetrakis(dimethylamido)titanium / oxygen plasma, respectively. Other possible precursors would be triethylaluminum / oxygen plasma or titanium isopropoxide / water, respectively.Other thin-film deposition techniques, alternatives to ALD, could also be used, provided they result in extremely smooth surfaces, the desired thicknesses can be precisely controlled, and the coating is conformal on all facets of the nano- or microwire.

[0023] The thick layer that guides the light emitted by Ga2O3:Cr (stage ¡ib) has a thickness sufficient to guide the light; for example, 400 nm.

[0024] The long trench made in stage 4 using FIB has suitable dimensions, for example, 5 x 3 x 3 pm. A -45° ramp is suitable on the side, facilitating the detection of resonant modes.

[0025] Note that in the fabrication process of this device, a large number of nano- or microwires can be deposited on the substrates, and ALD coats them all simultaneously in a single device processing step. Therefore, more than one of these resonant microcavities with identical DBRs can be fabricated on the same substrate. However, in step iii), although not scalable, it can be performed in as many structures as desired, resulting in secondary microcavities that are part of the final device and can also be used as temperature sensors. This is valuable both for calibration purposes and to address unforeseen events in the event of device malfunction, which would improve production efficiency. The atomic layer deposition (ALD) technique enables the controlled production of thin films and is widely used in semiconductor device fabrication.It is based on sequential, self-limiting processes that alternate the deposition of two or more chemical precursors in a layer-by-layer growth mechanism. ALD offers precise control of layer thickness, good large-scale uniformity, and conformity across the different facets of a three-dimensional (3D) structure. A similar technique with similar characteristics is molecular layer deposition (MLD).

[0026] It should be noted that the substrate used as an example, Si, is compatible with other Si-based electronic components, and its dimensions can be reduced to a scale of a few microns (limited to the dimensions of the nano- or microwire + trench cavity) if necessary, for specific temperature measurement. The designed microthermometer combines: robustness with respect to physical contact, high radiation, or different environments (e.g., liquids); operability over a wide temperature range of several hundred degrees; and, finally, high resolution in temperature measurement, better than 0.5 K over a wide temperature range. Furthermore, simple calibration by fitting peak shifts to a cubic function and high reliability of peak shifts based on interferometry have been demonstrated.Finally, in the event of a malfunction, other optical microcavities present on the same chip can be used to correlate temperature readings or as a backup.

[0027] BRIEF DESCRIPTION OF THE DRAWINGS

[0028] To complement the description being made and in order to help better understand the characteristics of the invention, a set of drawings is attached as an integral part of said description, in which the following has been represented for illustrative and non-limiting purposes:

[0029] Figure 1. Diagram of the trench manufacturing process in three etching steps.

[0030] Figure 2. A) Side view of the multilayers and trenches forming the microthermometer, with the defined axes indicated; B) Microphotoluminescence (p-PL) images of a microcavity; C) SEM side view image (52° tilt) of the microwire before ALD encapsulation, with dimensions labeled and the defined axes indicated.

[0031] Figure 3. Schematic of the structure and operation of the microthermometer: (a) bulk substrate; (b) DBR structure; (c) film composed of a low refractive index material that allows guiding the light emitted by the nanowires or microwires; (d) nanowires or microwires; (e) film deposited after deposition of nanowires or microwires, composed of a low refractive index material that allows guiding the light emitted by the nanowires or microwires; (f) DBR structure after deposition of nanowires or microwires; (g) laser; (h) guided light; (i) target; (j) excitation point of the microwire; (k) collection point.

[0032] Figure 4. Typical p-PL spectrum of the device shown (A). Detail of the device (B). Comparison of the DBR reflectivity of the device shown from the experimental value and from FDTD simulations (C).

[0033] Figure 5. Position of one of the resonant p-PL peaks as the device temperature varies.

[0034] Figure 6. Variation of the position of the resonant p-PL peak as a function of temperature and cubic fitting (top). Fitting of the peak using Lorentzian functions at two temperatures that differ by only 0.4 K (bottom).

[0035] PREFERRED EMBODIMENT OF THE INVENTION

[0036] The present invention is illustrated by the following examples, which are not intended to be limiting of its scope.

[0037] Example 1.

[0038] This example concerns the manufacture of an interferometric luminescent meter.

[0039] According to the described method, elongated Ga2Ü3:Cr microstructures are synthesized following the method previously described by the inventors (Alonso-Orts, Manuel, et al., 2022) and, subsequently, the DBR substrate is fabricated by ALD on silicon, with dimensions of, for example, 0.1 x 0.1 cm. 2 or 0.5 x 0.5 cm 2 .

[0040] This DBR substrate is composed of a four-period AhOa - TiOp DBR structure and an Al2O3 film. The thickness of the Al2O3 - TiO2 layers is 113 nm for the Al2O3 layers and 75 nm for the TiO2 layers (for these thicknesses, the reflectivity under normal incidence of the light emitted by the cavity is around 70-80%, as shown in the lower part of Figure 4) while the thickness of the Al2O3 film is 400 nm.

[0041] Ga2O3:Cr nano- or microwires are deposited on the DBR substrate and located by electron / optical microscopy. A 5 x 3 x 3 pm trench is cut at the ends of these structures. The side of each trench, farthest from the wire, features a 45° ramp to facilitate the detection of resonant modes (brighter regions on both sides of the nano- or microwire, as seen in Figure 2).

[0042] The trenches are manufactured in three etching steps. Figure 1 shows a schematic cross-section of each step. First, a rectangle is carved; then, a slope with a triangular pattern is carved; and finally, the end face of the microwire is cleaned with an additional triangular carving.

[0043] Finally, a layer of Al2O3 is deposited on top and on the sides of the created structure. A new TiO2-Al2O3 DBR with three and a half periods (i.e., ending at TiO2) is also deposited, similar to the one described in the third paragraph of this example.

[0044] Figure 2 (top panel) shows a schematic of the microwire along with the trenches and multilayers that make up the thermometric device, specifying their materials and dimensions.

[0045] Example 2.

[0046] This example shows the characterization of the microthermometer manufactured as described in Example 1.

[0047] The bottom of Figure 2 shows a SEM image (bottom left panel) and a microphotoluminescence (p-PL) image (bottom right panel) of a microcavity of the device, which is used as an optical thermometer.

[0048] The SEM image shows the trenches along both ends of the nano- or microwire. The brighter contrasting regions around the device represent the layers formed by ALDs around it, which act as reflectors (DBRs) and almost completely confine the emitted light from the Ga2O3:Cr active region. The p-PL image in the right panel is filtered to show only the photoluminescence of the structure (without the presence of the excitation laser spot, which in this example is located at A = 442 nm). The light guiding, the strong confinement within the nano- or microwire, and the collection due to reflection in the aforementioned FIB trenches at the ends of the structure can be observed.Figure 3 shows a schematic of the complete device illustrating the steps described above and the illumination setup for excitation (e.g., by a 442 nm laser) of the luminescence and collection of the luminescence, such as by a 100x objective on a Horiba confocal microscope.

[0049] A typical p-PL spectrum of the device shown, recorded at room temperature (RT), is shown at the top of Figure 4. A large number of resonant maxima (modes) can be observed across the entire Ga2O3:Cr emission range (A = 670–780 nm), arising from interferometric phenomena in accordance with the dimensions of the ALD-fabricated DBRs. A detail of the previous spectrum is presented in the right panel, showing well-defined, intense, and fine peaks (full width at half maximum, FWHM = 0.4–0.5 nm), allowing their positions to be accurately read. Dividing the wavelength difference between two consecutive peaks (known as the free spectral range) by the FWHM of a peak, the so-called optical cavity finesse parameter can be calculated. This parameter is related to the energy stored in the system.In this example device, a high finesse value (F = 11.0 ± 1.0) is measured over the wavelength range A = 700 - 750 nm, indicating strong optical confinement in the desired spectral range and leading to an accurate reading of the position (the wavelength) where the maxima of the modes (the resonant lines) are located. From the fineness of the resonant peaks, the experimental value for the reflectivity of the DBRs at the wire ends is calculated (Suter, Martin and Dietiker, Peter. Calculation of the finesse of an ideal Fabry-Pérot resonator, Applied Optics 53.30 (2014) 7004-7010), resulting in a value between 60% and 80% across the entire wavelength range of interest, as shown in Figure 4C (blue dots in the graph).For completeness, the same figure shows the simulated reflectivity using the finite difference time domain (FDTD) method of a model of the same optical cavity in blue line, which reasonably fits the experimental data.

[0050] The positions of the resonant modes shift with changing ambient temperature. This is due to the change in the refractive index of the Ga2O3:Cr material of which the microcavity is constructed with temperature, as well as thermal expansion, resulting in a slight elongation of the nano- or microwire dimensions. Furthermore, it is also possible to perform a second, simultaneous thermometric measurement, which arises from the native emission of the optical cavity material. In the example shown, Ga2O3:Cr displays so-called R-line emission, which are two very intense peaks at low temperatures and whose intensity decreases at high temperatures. Previous work (Mykhaylyk, Vitaliy, et al. Multimodal noncontact luminescence thermometry with Cr-doped oxides, Sensors 20.18 (2020): 5259), including our recently published work on FIB-fabricated microcavities (Alonso-Orts, Manuel, et al.Wide dynamic range thermometer based on luminescent optical cavities in Ga2O3: Cr Nanowires, Small 18.1 (2022): 2105355.) the intensity ratio or wavelength shift of the R lines of the Cr ion has been used. 3+ as a temperature sensor, which is accurate for temperatures around room temperature or lower.

[0051] On the other hand, the aforementioned resonant peaks due to DBR fabrication are more precise and remain very intense at all temperatures above ~90K, emphasizing the advantages of implementing the patented steps for detection over a wide temperature range with high accuracy.

[0052] Example 3

[0053] This example shows the operation of the device of the invention, manufactured according to example 1 as a microthermometer.

[0054] The thermometric capabilities are shown in Figure 5, exemplified by the resonant peak that appears in the range of 718 - 722 nm. In this experiment, the sample environment (a cryostat, in a vacuum of p = 10') 6mbar) was cooled to 94.5 K and then heated to 394.5 K, in both cases in 50 K steps (temperatures were measured independently using an Oxford Smart Temperature Monitor). The shift of the resonant maximum wavelength with respect to these known cryostat temperatures is shown in Figure 5. We show that the optical emission from our device can be directly correlated to temperatures from 94.5 K to 394.5 K by measuring the position of the resonant peak, i.e. its peak wavelength value at the desired temperature. These peak wavelength values ​​are obtained by fits to Lorentzian functions, and the measurement uncertainty of these fits, which is ±0.001 over the entire temperature range, can be related to the temperature resolution of our device, as shown below.It should be noted that the high-temperature end of the measurements was limited by our measurement setup. Ex situ heating tests (i.e., in a heater where the p-PL signal cannot be measured) have been performed, showing that the system can operate up to at least 600°C = 873 K without any observed changes in the system or any impact on its p-PL signal after heat treatment.

[0055] The shift of the peak wavelength relative to its value at room temperature (TA, or RT) of 295.0 K (which we define as AA = 0) is plotted against temperature in Figure 6 (top). The experimental data are closely fitted to a cubic function with temperature (AA = AT 3 + BT 2 + CT + AAo). In this example, the fitting parameters obtained are C = -0.0022 ± 0.0006) nm / KB = (2.6 ± 0.3)*10- 5 nm / K 2 , A = (- 0.9 ± 0.4)*10- 8 nm / K3 and AAo = (- 1.43 ± 0.04) nm. This cubic fit can be used as a calibration curve for the microthermometer, taking as initial value A = 720.334 nm (at TA = 295.0 K according to the calibration curve). Any unknown temperature can then be measured from it, with the uncertainty shown in Table 1 of example 4. Measurements have been performed in vacuum, but test measurements (for TA and higher) have also been carried out under atmospheric conditions, with equivalent results. The system could potentially be used in different gas atmospheres or even in liquids, since the oxide layers are non-reactive and protect the optical microcavity based on the gallium oxide nanowire or microwire.

[0056] Example 4

[0057] This example refers to the temperature resolution of the microthermometer in Example 1.

[0058] To demonstrate the resolving power of the microthermometer in temperature measurement, two temperatures differing by only 0.4 K = 0.4 °C were probed: 344.6 K = 71.5 °C and 345.0 K = 71.9 °C, and the p-PL signal from the microthermometer was measured. Figure 6 (bottom) shows the experimental results of this probing. The resonant peak positions and fitting uncertainties showed that the temperature difference of 0.4 K could be reliably determined in this case, since the peak position uncertainties of ±0.001 nm are clearly smaller than the shift (0.006 nm, in this example) of the resonant peak position when heating or cooling the environment by only four-tenths of a degree.

[0059] On the other hand, the temperature measurement resolution of thermometric readings improves as the temperature increases due to the aforementioned cubic temperature dependence of the resonant peak shift.

[0060] An estimate of the resolution for each temperature can be made by dividing the experimental error in the peak position, obtained by fitting a Lorentzian curve, by the temperature coefficient dA / dT. Table 1 shows the temperature coefficient and temperature resolution values ​​for our device, for the peak at 720.334 nm at RT (similar temperature resolutions are found for the other resonant peaks). Lorentzian fits for these curves are available from researchers upon request. Note that published apparent temperature measurements based on native emission from the material (i.e., the Ga2O3:Cr R lines) have a resolution of ±0.5 K or worse over the 50–150 K range.This means that, assuming a high-resolution diffraction grating (0.001 nm wavelength step or better) is used, the interferometric microthermometers of this invention have considerably better temperature resolution (±0.1 K for temperatures above 194.5 K and between ±0.2 K and ±0.4 K at low temperatures) than GajC^Cr thermometers over the entire temperature range. The native emission from the material could be used at cryogenic temperatures as an accurate complementary secondary temperature readout.

[0061] Table 1

[0062] Furthermore, it should be noted that after increasing the temperature by, for example, 0.4 K (Figure 6), when it is reduced back to the original value, the microthermometer measures the original peak position (with an uncertainty of ±0.001 nm), i.e. the interferometric microcavity does not suffer from thermal hysteresis and can therefore be used reversibly to measure both heating and cooling processes, with the high temperature resolution mentioned above.

[0063] Example 5.

[0064] This example concerns the robustness of the microthermometer manufactured according to example 1.

[0065] Measurements are performed with different laser excitation powers on the device to assess its robustness and the results are compared with those of other devices. While the GajC^Cr microthermometer manufactured by FIB previously (Alonso-Orts, Manuel, et al. Wide dynamic range thermometer based on luminescent optical cavities in Ga2O3. Cr Nanowires, Small 18.1 (2022): 2105355) degrades when using an excitation power higher than 3.5 mW at 442 nm, the same laser can be used in the ALD-FIB microthermometer of the present invention up to four times this value, i.e., up to an excitation of 14 mW, without any sign of device malfunction. In fact, the microthermometer heats up less than 10 K at such a high laser power while the microthermometer manufactured by FIB heats up more than 200 K when applying an excitation of 3.5 mW.This highlights the ability of the microthermometer presented here to withstand intense radiation from lasers or other sources, making it attractive for, for example, aerospace applications.

[0066] DBRs, formed by oxide layers deposited around the nano- or microwire, also prevent the microcavity from detaching from its substrate or breaking up upon physical contact or exposure to liquids such as water or ethanol, indicating their potential use in in vitro conditions or in temperature measurements involving liquid-solid interfaces.

Claims

CLAIMS 1. Luminescent and interferometric microthermometer based on GajC^Cr nanowires or microwires comprising: a) A layer of massive substrate b) A layer deposited on the massive substrate, of nanometric thickness, with a Bragg reflector structure DBR of n periods (n being an integer or half-integer), and composed of two materials transparent to the light to be confined, but whose combination in the aforementioned DBR behaves as an efficient reflector of said light. c) A sheet deposited on layer b), of greater thickness than it and composed of a low refractive index material that allows guiding the light emitted by the Ga?O3:Cr d) Nanowires or microwires of Ga2O3:Cr, previously grown, deposited on sheet c) that, when excited, emit light in the red-near infrared range, in the range between 600 nm and 900 nm.e) A new layer c) deposited on the nanowires or microwires d) and which is parallel to each of its surfaces, both the upper and the lateral ones, defined by the three axes x, y, z f) A new layer of DBR b) deposited on the layer e) which is also parallel to each of the surfaces of the nanowires or microwires, defined by the three axes x, y, z, including those of the final ends.

2. Microthermometer, according to claim 1, where the massive substrate is a silicon wafer.

3. Microthermometer, according to claim 2, wherein the massive substrate layer a) has dimensions of 0.5 x 0.5 cm 2 .

4. Microthermometer, according to claims 1 and 2, wherein the first DBR structure b) is composed of AI2O3 - TÍÜ2.

5. My erotherm or meter, according to claim 4, where the DBR structure has 4 periods (n = 4) and thicknesses of 113 nm for the AI2O3 layers and 75 nm for the TIO? layers.

6. Microtherm or meter, according to previous claims, where the thick layer c) that guides the light emitted by the Ga2Ü3:Cr is composed of AI2O3 7. Microthermometer, according to claim 6, where layer c) has a thickness of 400 nm.

8. Method for manufacturing a luminescent and interferometric microthermometer based on Ga2Ü3:Cr nanowires or microwires comprising: i. Obtaining Ga2Ü3:Cr nanowires or microwires as elongated structures that form the optical cavity. i. Fabrication of the DBR substrate using the ALD technique on a massive substrate which, in turn, comprises: a) A nanometric thickness DBR, with a structure of n-period Bragg reflectors (n being an integer or half-integer), and composed of two materials transparent to the light to be confined. b) A sheet of low refractive index material, essential for guiding the light emitted by the Ga2O3:Cr. iii. Deposition of the elongated structures obtained in step / on the DBR substrate obtained in step / / . iv.v. Depositing a thick material with a low refractive index plus an n-period DBR, equivalent to step 77, on the upper part and lateral surroundings of the structure obtained in step iv.

9. Method according to claim 8, wherein the DBR substrate obtained in step / / is manufactured on a silicon substrate.

10. Method according to claim 8, wherein the first nanometric thickness DBR structure is composed of AI2O3 - T¡O2.

11. Method according to claim 10, wherein the deposition of the AI2O3 and TIO2 layers is carried out by ALD (atomic layer deposition).

12. Method according to claim 11, wherein the deposition of layers of AI2O3 and T¡Ü2 is carried out by ALD using precursors.

13. Method according to claim 12, wherein the precursors for the deposition of AI2O3 and TIO2 layers by ALD are trimethylaluminum / water, and tetrakis(dimethylamido)titanium / oxygen plasma, respectively.

14. Method according to claim 12, wherein the precursors for the deposition of AI2O3 and TÍÜ2 layers by ALD are thetilaluminium / oxygen plasma or titanium isopropoxide / water, respectively.

Images