Materials for sensor applications

Abstract

A thermal resistance sensor comprising a substrate, a structure bonded to the substrate, and a niobium oxide layer bonded to the structure.

Description

[Technical Field]

[0001] This disclosure relates to materials for sensors, and more particularly to the use of niobium oxide (NbOx) as a sensor material. [Background technology]

[0002] Uncooled thermal resistance sensors, including microbolometers, thermistors, and passive infrared (PIR) motion sensors, can utilize resistive conversion from heat to current or voltage. The performance and stability of these devices are inevitably determined by the sensor material. These resistive materials can exhibit a higher temperature coefficient of resistance (TCR), while being limited by excess noise (e.g., 1 / f in character). These devices may also be used to convert a fixed bias voltage to a current output (and vice versa), where the change in output arises from a change in the temperature of the resistor. [Overview of the Initiative] [Problems that the invention aims to solve]

[0003] This disclosure discloses thermal resistance sensors such as microbolometers, thermistors, and PIR motion sensors. [Means for solving the problem]

[0004] In one implementation form, a thermal resistance sensor is disclosed. The sensor includes a substrate, a structure bonded to the substrate, and a niobium oxide layer bonded to the structure.

[0005] In another implementation, a microbolometer sensor for thermal imaging is disclosed. The microbolometer sensor includes a substrate, a structure bonded to the substrate but positioned to be thermally isolated from the substrate, and pixels bonded to the structure, the pixels comprising a niobium oxide layer.

[0006] In another implementation, a microbolometer sensor for thermal imaging is disclosed. The microbolometer sensor comprises a niobium oxide material having a metal-to-insulator transition (MIT) temperature above 400°C and a temperature coefficient of resistance (TCR) of 2–5% at room temperature.

[0007] Other features and advantages will become apparent from this specification, which illustrates various aspects of this disclosure as examples.

[0008] Details of this disclosure, both in terms of structure and operation, can be partially gathered by studying the accompanying drawings, where similar reference numbers refer to similar parts. [Brief explanation of the drawing]

[0009] [Figure 1] This figure shows exemplary transition temperatures for different materials, including NbO2 and VO2. [Figure 2] This diagram illustrates an example sensor in one implementation configuration. [Figure 3] This figure shows noise measurement data and associated Hooge parameters for an exemplary NbOx sensor. [Figure 4] This figure shows exemplary NbOx sensor TCR data that remains unchanged over several weeks. [Figure 5] This figure shows noise measurement data and associated Hooge parameters for an exemplary Ti-doped NbOx sensor. [Figure 6] This figure shows TCR data from an exemplary Ti-doped NbOx sensor. [Figure 7] This figure shows the signal-to-noise ratio data for exemplary NbOx sensors and Ti-doped NbOx sensors. [Figure 8] This figure illustrates the exemplified dependence of resistivity during reactive sputtering on the partial pressure of O2. [Figure 9] This figure shows a performance comparison between exemplary sensors containing different materials. [Modes for carrying out the invention]

[0010] As mentioned above, conventional resistive sensor materials for microbolometers can exhibit higher TCRs, although limited by excess noise (e.g., 1 / f of character). These microbolometers may use amorphous silicon, which can limit performance due to higher 1 / f noise and a more restrictive temperature stability window. If noise is reduced by crystallizing part of the amorphous network or lowering its resistivity (e.g., by increasing crystallinity or doping), the TCR may drop below acceptable levels. Some uncooled bolometers use vanadium oxide (Vox or VO2), which can have better metrics while maintaining higher TCR values. However, depending on the phase, the metal-insulator transition (MIT) of VOx can be around 65-85°C. This allows VOx to be used to limit the operating temperature of the device to near or below the transition temperature. Materials such as quantum wells, graphene, and carbon nanotubes can be used for thermal sensing, but these materials may not be suitable considering manufacturability.

[0011] A particular implementation of this disclosure provides a microbolometer that uses niobium oxide (NbOx) as a sensor material. In one implementation, NbOx refers to niobium monoxide (NbO), niobium pentoxide (Nb2O5), or preferably niobium dioxide (NbO2). The preferred target is NbO2 based on the desired film properties and the physical nonstoichiometric properties of the amorphous material, although the actual Nb / O ratio does not have to be exactly 2, but rather may be between 1.8 and 2.2.

[0012] In one implementation, the transition temperature of NbO2 is above 400 °C, and this transition temperature may make NbO2 a less suitable material for switching applications operating near room temperature. However, some microbolometer implementations can benefit from a transition temperature that is significantly higher than the operating temperature. In one implementation, this high transition temperature enables a higher dynamic range of operation for some thermal resistance applications. For example, a high-temperature object in a scene will not push the pixel temperature above the transition in a microbolometer using NbO2.

[0013] After reading the following description, a method for implementing the present disclosure in various implementations and applications will become apparent. Although various implementations of the present disclosure are described herein, it is understood that these implementations are presented by way of example only and are not limiting. Accordingly, the detailed description of the various implementations should not be construed as limiting the scope or breadth of the present disclosure.

[0014] As described above, there are multiple factors that make a promising candidate for use in a microbolometer. The factors include a high TCR, low 1 / f noise, process compatibility, manufacturability into thin films, appropriate resistivity, and a high transition temperature.

[0015] FIG. 1 shows exemplary transition temperatures of different materials including NbO2 and VO2. FIG. 1 clearly shows that NbO2 is a promising candidate based on its high transition temperature while meeting the other factors described above.

[0016] In one implementation, the sensor includes a non-cooled microbolometer for thermal imaging in long-wave infrared (LWIR), mid-wave infrared (MWIR), or short-wave infrared (SWIR). In another implementation, the sensor includes an antenna-coupled non-cooled microbolometer sensor for terahertz sensors. In another implementation, the sensor includes a low-noise thermistor. In another implementation, the sensor includes a passive infrared (PIR) sensor. In one implementation, the sensor has an operating temperature range of -40°C to 345°C. In one implementation, the sensor may not be damaged when exposed to or imaging a high-temperature source such as the sun.

[0017] In one implementation, the upper limit of the operating temperature (ambient) of the microbolometer using the NbOx sensor can be established as follows. The microbolometer that forms an image on an object within the field of view can have a temperature transfer ratio of 1 / 100. That is, when the surface temperature of the object is T_object, the pixel temperature rises by T_object / 100 from the ambient temperature. The operating temperature T_op is directly added to the pixel temperature, and thus the pixel temperature can be T_op + T_object / 100. When the object is the sun with a surface temperature of 5500°C, the requirement that the pixel temperature remains below the material's transition temperature (400°C) results in an upper limit of the operating temperature T_op < 345°C. In practice, the operating temperature can be significantly lower than this.

[0018] In one implementation, the sensor has a resistivity range of 1 to 100 ohm-cm at room temperature, which can enable the desired noise equivalent temperature difference (NETD) as follows. The resistivity range can be set based on the requirements of the readout circuit related to geometric factors of the pixel such as the pixel pitch and thickness. In one implementation, the resistivity range is achieved by intrinsic non-stoichiometry, with a low x resulting in a low resistivity. In one implementation, the resistivity range is achieved using external doping with at least one of other suitable dopants such as titanium (Ti), molybdenum (Mo), and chromium (Cr).

[0019] In one implementation configuration, the sensor includes an LWIR, MWIR, or SWIR microbolometer sensor, and the complex refractive index of the sensor provides sufficient absorption to convert the radiated input into heat.

[0020] In one implementation configuration, the sensor advantageously achieves the desired pixel resistance, 1 / f noise power, TCR, and material stability. In one implementation configuration, the sensor performance is expressed in NETD, and the desired sensor parameters can achieve the desired NETD (lower numbers are more desirable). NETD can be expressed as a function of the bolometer and camera parameters as follows:

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[0021] In one implementation configuration, the thermal isolation capability of a pixel is characterized by the pixel's thermal conductance, which is primarily controlled by Gth (unit = W / °K), the geometry (width, thickness, length) of the hinge that suspends the pixel on the substrate, and the material and vacuum level used for the hinge. A lower Gth results in a greater temperature rise for a given amount of absorbed energy. Regarding the design and fabrication of pixels, the hinge needs to be narrower and / or thinner to compensate for the shorter hinge resulting from the reduced pixel pitch. Scaling Gth can also help as pixels become smaller and limit the ability of the lens to be faster (smaller F / #).

[0022] In one implementation configuration, the sensor favorably exhibits lower 1 / f noise when quantified by Hooge parameters (i.e., K×V<5×e -22 cm 3 (wherein K is the measured 1 / f noise shown in equation [1], which is determined by the resistance sensor material, and V is the volume of the sample). The Hooge parameter is a material-dependent parameter that allows for noise comparison between materials. Since the noise of the device decreases as the size of the device increases, the Hooge parameter is used as a means of normalizing the size effect.

[0023] Figure 3 shows an exemplary NbO x The sensor noise measurement data and associated Hooge parameters are shown. Figure 3 is a graph of the noise as a function of frequency, and the dependency is linear on a log-log scale. This graph shows that when normalized to the applied voltage, all of the device's noise values ​​directly overlay. Thus, this graph provides confidence in the measured values ​​for noise. The Hooge parameters are then calculated by multiplying the noise measured here (i.e., the K value, which is the y-axis value at 1 Hz) by the volume of the sensor in the device (not shown in the graph).

[0024] Figure 4 shows an exemplary NbO xShows the TCR data of the sensor. In one implementation, the TCR data preferably remains unchanged over several weeks. The TCR value obtained from this graph can be used in Equation [1]. Thus, the graph of FIG. 4 shows that this material (i.e., NbO x ) is suitable for temperature sensing applications.

[0025] There are other materials that exhibit low noise (i.e., a small Hooge parameter), but a significant number of those materials are metals that exhibit (a) a very low TCR value and (b) a very low resistivity for any practical application. There are also other materials that exhibit a very high TCR value, but a significant number of those materials are (a) extremely resistive and (b) very noisy (i.e., a high Hooge parameter). NbOx has been shown to provide both low noise and a high TCR value simultaneously.

[0026] FIG. 5 shows the noise measurement data and the associated Hooge parameter of an exemplary Ti-NbO x sensor. In FIG. 5, NbOx is doped with a titanium dopant (Ti-). FIG. 5 shows that the noise remains low even when doped with / alloied with another metal that causes a change in resistivity.

[0027] FIG. 6 shows the TCR data of an exemplary Ti-NbO x sensor and shows that the TCR value can be adjusted by external doping / alloying like resistivity. However, it should be noted that the resistivity and TCR can be controlled using different methods such as directly controlling the Nb / O ratio.

[0028] FIG. 7 shows the signal-to-noise ratio data of an exemplary NbO x sensor and a Ti-NbO x sensor. The graph of FIG. 7 here

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[0029] In one implementation configuration, undoped NbOx can improve the signal-to-noise ratio by reducing its resistivity and / or TCR to unsuitable ranges for some applications. In another implementation configuration, the addition of Ti can advantageously increase the TCR while reducing noise. In yet another implementation configuration, Cr is added to lower the resistivity of NbOx materials with high oxygen content.

[0030] In one implementation configuration, the sensor includes an amorphous or polycrystalline thin film of NbOx. For example, the sensor is NbO x This includes amorphous thin films or polycrystalline thin films. In one implementation, the sensor is configured to not change phase (e.g., from metal to insulator) within a temperature range of, for example, -40 to 345°C. In one implementation, the temperature range is related to deviations during the packaging process. In one implementation, the temperature range is related to temperature deviations during sensor operation.

[0031] In one implementation, NbO x It is suitable for silicon processing and / or glass substrate semiconductor processing (e.g., PVD or CVD). In one mounting configuration, NbO x The TCR has a TCR of 2-5% (preferably 2-3%), which can favorably meet the TCR requirements for achieving the desired NETD and can be controlled by the deposition and annealing processes during sensor manufacturing. In one implementation configuration, deposition includes one or more of the following: reactive sputtering, molecular beam epitaxy (MBE), metal-organic chemical vapor deposition (MOCVD), atomic layer deposition (ALD), physical vapor deposition (PVD), electrochemical deposition, sol-gel method, and other thin film deposition methods.

[0032] Figure 8 shows an exemplary dependence of resistivity during reactive sputtering on the partial pressure of O2. The graph in Figure 8 shows resistivity as a function of both oxygen content and thermal process, and the resistivity is not dominated by either, but rather by the scale. The graph shows that conductive oxides do not have to be overly sensitive to subsequent processes such as high-temperature steps and do not have to limit the acceptable properties of the film. This means that NbOx can have its resistivity tuned without the need for external dopants. The graph also shows that subsequent thermal processing can have a small but decisive effect, such as the type required for vacuum packaging.

[0033] Figure 9 is a graph showing a performance comparison between sensors made of different materials. In particular, the graph shows that the disclosed NbOx-based sensor can achieve performance similar to or better than that of VOx, which has the aforementioned benefits.

[0034] Figure 2 is a block diagram of a thermal resistance sensor 200 according to one implementation configuration of the present disclosure. In one implementation configuration, the sensor 200 includes a substrate 230, a structure 220 coupled to the substrate 230, and pixels 210 coupled to the structure 220.

[0035] In one mounting configuration, the structure 220 is positioned so as to be thermally isolated from the substrate 230. In one mounting configuration, the pixel 210 includes a niobium oxide layer. In one mounting configuration, the sensor 200 receives a voltage difference and generates a current or charge based on the received radiation (i.e., the resistance between the two terminals of the sensor changes in response to exposure to LWIR or MWIR radiation).

[0036] In one implementation configuration, the thermal resistance sensor is a microbolometer, and its structure is thermally isolated from the substrate. In one implementation configuration, the thermal resistance sensor is a thermistor. In one implementation configuration, the thermal resistance sensor is a passive infrared (PIR) motion sensor. In one implementation configuration, niobium oxide is NbO2. In one implementation configuration, niobium oxide is NbOx. In one implementation configuration, niobium oxide is titanium-doped Ti-NbOx. In one implementation configuration, the niobium oxide layer is a pixel sensor.

[0037] In one particular implementation, a microbolometer sensor for imaging is disclosed. The microbolometer sensor includes a substrate, a structure bonded to the substrate, and pixels bonded to the structure, the pixels comprising a niobium oxide layer.

[0038] In one implementation configuration, the sensor is used for thermal imaging in the infrared (IR) region. In one implementation configuration, the IR region includes at least one of long-wavelength infrared (LWIR), medium-wavelength infrared (MWIR), and short-wavelength infrared (SWIR). In one implementation configuration, the sensor has an operating range of -40°C to 345°C. In one implementation configuration, the sensor further includes a readout circuit. In one implementation configuration, the sensor has a resistivity range set based on the geometric factors of the pixels and the requirements of the readout circuit. In one implementation configuration, the geometric factors of the pixels include the pixel pitch and thickness. In one implementation configuration, the resistivity range is achieved using external doping with at least one of titanium (Ti), molybdenum (Mo), and chromium (Cr). In one implementation configuration, the sensor has a resistivity range of 1 to 100 ohms / cm at room temperature. In one implementation configuration, the structure is a hinge assembly that thermally separates the pixels from the substrate.

[0039] In another specific implementation, a microbolometer sensor for thermal imaging is disclosed. The microbolometer sensor comprises a niobium oxide material having a metal-insulator transition (MIT) temperature above 400°C and a temperature coefficient of resistance of 2–5% at room temperature.

[0040] In one implementation configuration, the niobium oxide material has a resistivity of 1 to 100 ohms / cm at room temperature. In one implementation configuration, the microbolometer sensor further includes a substrate and a structure bonded to the substrate, the structure being a set of hinges that thermally separate the niobium oxide material from the substrate.

[0041] In one implementation, the sensor includes a glass substrate, a structure manufactured from one of the methods described herein and bonded to the glass substrate, and pixels bonded to the structure. The pixels include materials described herein.

[0042] In one implementation configuration, the sensor includes a MEMS or NEMS device manufactured by an LCD-TFT manufacturing process and a structure manufactured by any of the methods described herein.

[0043] For example, various sensors can include resistance sensors. Bolometers (or microbolometers) can be used in a variety of applications. For example, long-wave infrared (LWIR, wavelengths of approximately 8-12 μm) bolometers can be used in the automotive and commercial security industries. For example, LWIR bolometers with QVGA, VGA, and other resolutions. Terahertz (THz, wavelengths of approximately 1.0-0.1 mm) bolometers can be used in security (e.g., airport passenger security screening) and medical (medical imaging). For example, THz bolometers with QVGA resolution and other resolutions. Some electronic or electro-optical systems can include X-ray sensors or camera systems. Similarly, LWIR and THz sensors are used in camera systems. Some electrochemical systems are applied to medical imaging such as endoscopes and exoscopy. X-ray sensors include direct sensing and indirect sensing configurations.

[0044] Those skilled in the art will recognize that the packaging configurations described herein are representative, and that any deviation from the expressly disclosed packaging configurations falls within the scope of this disclosure. For example, one packaging configuration may involve the use of a different dopant than those described. As another example, the manufacturing temperature (e.g., growth temperature) may be controlled to control the morphology and / or dopant efficiency. As yet another example, after deposition, the material may undergo additional processing such as annealing and / or laser-induced crystallization.

[0045] While the disclosed implementations are fully described with reference to the accompanying drawings, it should be noted that various changes and modifications will be apparent to those skilled in the art. Such changes and modifications should be understood to fall within the scope of the disclosed implementations as defined by the attached claims.

[0046] The terminology used herein to describe various implementations is intended to describe, and not to limit, specific implementations. Where used in the descriptions of various implementations and in the accompanying claims, the singular forms "a," "an," and "the" are intended to include the plural unless otherwise clearly indicated in the context. The term "and / or" as used herein will also be understood to refer to and encompass any possible combination of one or more of the related enumerated items. The terms "includes" and / or "including," where used herein, indicate the existence of a particular feature, integer, step, operation, element, and / or component, but will not exclude the existence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. The term "exemplary," where used herein, will also be understood to refer to something that functions as an example, instance, or illustration, or as a pattern, rather than something worthy of praise.

[0047] Not all features of each of the examples described above are necessarily required for any particular implementation of the present disclosure. Furthermore, it should be understood that the descriptions and drawings presented herein are representative of the subject matter broadly envisioned by the present disclosure. The scope of the present disclosure may be apparent to those skilled in the art, and therefore, it should be further understood that the scope of the present disclosure is not limited by anything other than the appended claims.

Claims

1. substrate, The structure bonded to the substrate, and Niobium oxide layer bonded to the above structure A thermal resistance sensor equipped with the following features.

2. The sensor according to claim 1, wherein the thermal resistance sensor is a microbolometer and the structure is thermally separated from the substrate.

3. The sensor according to claim 1, wherein the thermal resistance sensor is a thermistor.

4. The sensor according to claim 1, wherein the thermal resistance sensor is a passive infrared (PIR) motion sensor.

5. The niobium oxide is NbO ｘ The sensor according to claim 1.

6. The aforementioned niobium oxide is titanium-doped Ti-NbO ｘ The sensor according to claim 1.

7. The sensor according to claim 1, wherein the niobium oxide layer is a pixel sensor.

8. A microbolometer sensor for imaging, wherein the microbolometer sensor is substrate, The structure bonded to the substrate, and Pixels coupled to the aforementioned structure Equipped with, A microbolometer sensor in which the aforementioned pixels include a niobium oxide layer.

9. The microbolometer sensor according to claim 8, wherein the sensor is used for thermal imaging in the infrared (IR) region.

10. The microbolometer sensor according to claim 9, wherein the IR region includes at least one of long-wavelength infrared (LWIR), medium-wavelength infrared (MWIR), and short-wavelength infrared (SWIR).

11. The microbolometer sensor according to claim 8, wherein the sensor has an operating range of -40°C to 345°C.

12. The microbolometer sensor according to claim 8, further comprising a readout circuit.

13. The microbolometer sensor according to claim 12, wherein the sensor has a range of resistivity set based on the geometric factors of the pixel and the requirements of the readout circuit.

14. The microbolometer sensor according to claim 13, wherein the geometric factors of the pixel include the pitch and thickness of the pixel.

15. The microbolometer sensor according to claim 13, wherein the resistivity range is achieved by external doping with at least one of titanium (Ti), molybdenum (Mo), and chromium (Cr).

16. The microbolometer sensor according to claim 13, wherein the sensor has a resistivity in the range of 1 to 100 ohms cm at room temperature.

17. The microbolometer sensor according to claim 10, wherein the structure is a hinge set for thermally separating the pixels from the substrate.

18. A microbolometer sensor for thermal imaging, Niobium oxide material having a metal-insulator transition (MIT) temperature above 400°C and a temperature coefficient of resistance of 2-5% at room temperature. Microbolometer sensors, including [specific component].

19. The microbolometer sensor according to claim 18, wherein the niobium oxide material has a resistivity of 1 to 100 ohms cm at room temperature.

20. substrate, and Structure bonded to the aforementioned substrate Furthermore, The microbolometer sensor according to claim 18, wherein the structure is a hinge set for thermally separating the niobium oxide material from the substrate.

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