All-diamond pressure sensor, preparation method and dynamic temperature compensation method

Abstract

The present application relates to the technical fields of semiconductor sensor manufacturing, and particularly relates to a full diamond pressure sensor, a preparation method and a dynamic temperature compensation method, which comprises the following steps: in-situ integrating a serpentine platinum resistance temperature sensor on a stress-free area around a full diamond sensitive diaphragm, calibrating the full diamond sensitive diaphragm within 25-500 DEG C, and obtaining a first corresponding relationship between temperature and resistance value through least square fitting; applying a standard pressure at different temperatures, measuring the output voltage of a bridge composed of boron-doped diamond pressure-sensitive resistors; calculating the zero-point output and sensitivity at different temperatures, and respectively performing quadratic polynomial fitting to obtain the zero-point temperature drift and the sensitivity temperature fitting coefficient; and based on the first corresponding relationship and the fitting coefficient, a signal processing chip is used to perform real-time temperature compensation on the original electric signal. The present application realizes ultra-high precision pressure measurement with high-temperature temperature drift within 0.02% FS / ℃ in a full range.

Description

Technical Field

[0001] This invention relates to the field of semiconductor sensor manufacturing technology, and more specifically, to an all-diamond pressure sensor, its preparation method, and a dynamic temperature compensation method. Background Technology

[0002] In extreme and harsh operating conditions such as aerospace, petrochemical, and nuclear power, pressure sensing devices need to withstand the combined effects of high temperature, high pressure, and strong corrosion for extended periods. Diamond, due to its extremely high thermal stability, excellent chemical inertness, and sensitive piezoresistive effect, has become the core sensing material for manufacturing homogeneous, integrated all-diamond pressure sensors for extreme conditions.

[0003] However, the piezoresistive coefficient of diamond material itself exhibits a highly significant temperature dependence, easily leading to spontaneous drift in the resistance of the piezoresistor under extreme high-temperature environments. Because it is impossible to obtain accurate micro-area temperature in situ and in real-time within the pressure-sensitive region, the temperature drift in the sensor's output voltage signal is deeply coupled with the pressure excitation, making it difficult to establish an accurate temperature-pressure decoupling mapping relationship. This makes it difficult to eliminate zero-point drift and sensitivity temperature drift under high-temperature conditions, severely limiting the measurement accuracy of all-diamond pressure sensors in high-temperature environments. Summary of the Invention

[0004] The purpose of this invention is to provide an all-diamond pressure sensor, its fabrication method, and a dynamic temperature compensation method. By integrating a platinum resistance thermometer in an on-chip stress-free area to collect micro-area temperature in situ, and combining it with a quadratic polynomial fitting algorithm to decouple the zero point and sensitivity in real time, ultra-high precision measurement with extremely low high-temperature drift is achieved.

[0005] This invention is achieved through the following technical solution: A dynamic temperature compensation method for an all-diamond pressure sensor includes: Temperature characteristics of the on-chip platinum resistance temperature sensor of the all-diamond pressure sensor are calibrated. Based on the calibration data, the first correspondence between the real-time temperature and the resistance value of the on-chip platinum resistance temperature sensor is obtained by least squares fitting. At different calibration temperature points, standard pressures of different gradients were applied to the all-diamond pressure sensor, and the output voltage of the Wheatstone bridge in the all-diamond pressure sensor was measured. Based on the output voltage, the zero-point output and sensitivity of the all-diamond pressure sensor at different calibration temperatures were calculated, and the relationship between the zero-point output and sensitivity and temperature was fitted by a quadratic polynomial to obtain the zero-point temperature drift fitting coefficient and the sensitivity temperature fitting coefficient. The zero-point temperature drift fitting coefficient and the sensitivity temperature fitting coefficient are stored in the signal processing chip. The signal processing chip is then used to perform real-time temperature compensation on the original electrical signal of the Wheatstone bridge based on the first correspondence, the zero-point temperature drift fitting coefficient, and the sensitivity temperature fitting coefficient. The temperature drift error is then deducted, and the dynamically compensated pressure value is output.

[0006] Optionally, temperature characteristic calibration is performed on the on-chip platinum resistance temperature sensor of the all-diamond pressure sensor, including: Multiple uniformly distributed temperature points were selected within the range of 25℃ to 500℃; At each temperature point, maintain the temperature for a preset time. After thermal equilibrium is reached, measure the resistance value of the on-chip platinum resistance temperature sensor.

[0007] Optionally, there are 10 evenly distributed temperature points, with a preset time of 30 minutes.

[0008] Optionally, at different calibration temperature points, standard pressures of different gradients are applied to the all-diamond pressure sensor, including: At each calibrated temperature point, multiple standard pressure points within the full-scale range of 0 kPa to 170 kPa were applied to the all-diamond pressure sensor. The output voltage of the Wheatstone bridge at various standard pressure points was collected.

[0009] Optional, multiple standard pressure points, up to 18 standard pressure points.

[0010] Optionally, a quadratic polynomial fitting is performed on the relationship between zero-point output and sensitivity and temperature, including: The output voltage at each calibrated temperature point with a standard pressure of 0 kPa is extracted as the zero-point output. A quadratic polynomial equation for the zero-point output as a function of temperature is constructed and fitted to obtain the zero-point temperature drift fitting coefficient. The slope of the output voltage change with pressure at each calibration temperature point is extracted as the sensitivity. A quadratic polynomial equation of the sensitivity change with temperature is constructed and fitted to obtain the sensitivity temperature fitting coefficient.

[0011] Optionally, real-time temperature compensation controls the temperature drift of the all-diamond pressure sensor to within 0.02% FS / ℃ across the entire pressure range.

[0012] An all-diamond pressure sensor, comprising: A single-crystal diamond substrate is used. The back and front sides of the single-crystal diamond substrate are etched to form a beam-island-film composite structure sensitive film. The beam-island-film composite structure sensitive film includes a central rigid island, four-way support beams distributed in a cross-shaped symmetrical manner, and a stress-free area around the four-way support beams. Multiple boron-doped diamond varistors were grown in situ and etched into the region of maximum principal stress concentration at the root of a four-way support beam, with the long axis of each boron-doped diamond varistor aligned along the single-crystal diamond substrate. <110> Crystal orientations are interconnected to form a Wheatstone bridge; The on-chip platinum resistance temperature sensor adopts a serpentine structure design and is integrated in the stress-free area around it for in-situ acquisition of the real-time temperature of a single-crystal diamond substrate. The metal electrode layer is electrically connected to the boron-doped diamond varistor and the on-chip platinum resistance temperature sensor.

[0013] A method for fabricating an all-diamond pressure sensor, comprising: A single-crystal diamond substrate was selected, and a boron-doped diamond film was grown in situ on its front side using microwave plasma chemical vapor deposition as a piezoresistive sensitive layer. The crystal orientation of the piezoresistive sensitive layer was determined by electron backscatter diffraction. Based on the measured crystal orientation, a layer was formed along the crystal orientation using photolithography and inductively coupled plasma dry etching. <110> Four boron-doped diamond varistors with symmetrical crystal orientation are interconnected to form a Wheatstone bridge. Using an ultrashort pulse femtosecond laser, selective etching is performed on the back and front sides of a single-crystal diamond substrate to precisely form a central rigid island, a four-way support beam, and a stress-free area around the perimeter, resulting in a beam-island-film composite structure sensitive film. A Ti / Pt / Au three-layer metal was deposited on the piezoresistive sensitive layer and patterned to form the interconnects and lead-out electrodes of the Wheatstone bridge. The layer was then annealed in an inert atmosphere at 400°C to generate a stable TiC transition layer at the Ti-diamond interface. A high-purity platinum layer is deposited in the stress-free area around the chip and photolithographically formed into a serpentine platinum resistor, which serves as an on-chip platinum resistance temperature sensor.

[0014] Optionally, the overall size of the single-crystal diamond film is 800μm×800μm, and the thickness is 20μm; The central rigid island has dimensions of 200μm × 200μm and a thickness of 50μm; Each four-way support beam measures 300μm in length, 40μm in width, and 30μm in thickness.

[0015] The technical solution of the present invention has at least the following advantages and beneficial effects: This invention integrates a serpentine on-chip platinum resistance temperature sensor in situ within a stress-free region around an all-diamond sensitive diaphragm, placing it in the same micro-region thermal field as the piezoresistor, thus ensuring extremely high thermal inertia consistency. By acquiring the resistance value of the on-chip platinum resistance and using the least squares method and quadratic polynomial fitting to derive the zero-point temperature drift and sensitivity temperature fitting coefficients, the resistance drift caused by spontaneous temperature fluctuations can be subtracted from the output signal of the Wheatstone bridge in real time and with high accuracy. Based on a deeply integrated hardware and software in-situ compensation method, this invention completely breaks through the bottleneck of severe temperature-pressure signal coupling under extreme high temperatures, controlling the high-temperature drift of the device to an extremely low range across the entire pressure range, maximizing the high-precision measurement potential of the all-diamond pressure sensor under extreme temperature-pressure coupling conditions. Attached Figure Description

[0016] Figure 1 A flowchart of the dynamic temperature compensation method for the all-diamond pressure sensor provided by the present invention; Figure 2 This is a schematic diagram of the structure of the all-diamond pressure sensor provided by the present invention; Figure 3 A schematic diagram illustrating the fabrication method of the all-diamond pressure sensor provided by this invention; Legend: 1. Varistor, 2. Metal interconnect and pad, 3. Central rigid mass island, 4. Peripheral fixed support area, 5. Temperature sensor, 6. Square cantilever beam, 7. Diamond sensitive film. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0018] Example 1 This embodiment relates to a dynamic temperature compensation method for an all-diamond pressure sensor. In extreme and harsh operating conditions such as industrial, aerospace, nuclear power, and deep-earth drilling, pressure sensing devices typically need to withstand long-term exposure to high temperatures, high pressures, and strong corrosion from multiple physical field couplings. While the all-diamond pressure sensor, due to its homogeneous integrated design, avoids the risk of interface failure between heterogeneous materials, its on-chip piezoresistive resistor 1 experiences significant temperature drift when the operating temperature fluctuates widely. This is due to the strong temperature dependence of the piezoresistive coefficient of the diamond material, leading to severe nonlinear distortion in the final output voltage signal. To address this problem, such as... Figure 1As shown in the figure, this embodiment proposes a method for real-time, in-situ online compensation of temperature drift error, including the following steps: Temperature characteristics of the on-chip temperature sensor 5 of the all-diamond pressure sensor are calibrated. Based on the calibration data, the first correspondence between the real-time temperature and the resistance value of the on-chip temperature sensor 5 is obtained by least squares fitting.

[0019] Specifically, the calibration process involves placing the all-diamond pressure sensor, which integrates the on-chip temperature sensor 5, in a standard temperature-controlled heating furnace under stress-free conditions. Since the on-chip temperature sensor 5 is made of high-purity platinum, its resistance exhibits a highly consistent functional relationship with temperature. The specific temperature characteristic calibration process involves selecting multiple uniformly distributed temperature points within the range of 25℃ to 500℃. To ensure the representativeness of the temperature distribution, in this embodiment, 10 uniformly distributed temperature points are preferred, such as 25℃, 80℃, 135℃, 190℃, 245℃, 300℃, 355℃, 410℃, 465℃, and 500℃. After heating or cooling to each set temperature point, a preset holding time is applied at the corresponding temperature point to allow the sensor chip to reach sufficient thermal equilibrium with the ambient thermal field, eliminating measurement errors caused by temperature gradients inside and outside the chip. Preferably, this preset time is set to thirty minutes. Once the chip reaches complete thermal equilibrium, a high-precision multimeter measures and records the actual resistance value of the on-chip temperature sensor 5 at each calibrated temperature point in real time. After recording the resistance values ​​at all calibrated temperature points, with temperature as the independent variable and platinum resistance as the dependent variable, a linear or polynomial fit is performed using the least squares method to construct and output the first correspondence between the real-time temperature and the resistance value of the on-chip temperature sensor 5. This first correspondence can serve as the basis for subsequent sensor measurements during actual pressure measurements, enabling the sensor to convert the detected real-time resistance value of the platinum resistance into the true real-time temperature without hysteresis and with high accuracy.

[0020] At different calibration temperature points, standard pressures of varying degrees were applied to the all-diamond pressure sensor, and the output voltage of the Wheatstone bridge in the all-diamond pressure sensor was measured.

[0021] Specifically, to obtain the complex output characteristics of the sensor under the dual coupling of temperature and pressure, a temperature-pressure coupling calibration matrix needs to be established. In practice, at each preset calibration temperature point, a standard pressure load is applied to the diamond sensitive film 7 of the all-diamond pressure sensor using a high-precision pressure calibrator. The applied pressure range covers the sensor's designed full-scale operating range. In this embodiment, the applied standard pressure range is 0 kPa to 170 kPa. To obtain a sufficiently smooth and high-precision fitting surface and avoid interpolation distortion, 18 standard pressure points are uniformly selected and applied at each temperature point. Understandably, this embodiment selects pressures including 0 kPa, 10 kPa, 20 kPa, 30 kPa, 40 kPa, 50 kPa, 60 kPa, 70 kPa, 80 kPa, 90 kPa, 100 kPa, 110 kPa, 120 kPa, 130 kPa, 140 kPa, 150 kPa, 160 kPa, and 170 kPa. Under the temperature and pressure cross-condition formed by each combination of calibrated temperature and standard pressure, an on-chip external constant current or constant voltage source supplies power to a Wheatstone bridge consisting of four boron-doped diamond varistors 1 interconnected by metal interconnects and pads 2. A high-precision digital voltmeter is used to acquire and record the raw voltage output value of the Wheatstone bridge in real time. This output voltage value not only includes the effective component that changes linearly with pressure, but also deeply superimposed the zero-point drift error and sensitivity attenuation error caused by temperature fluctuations.

[0022] Based on the obtained output voltage, the zero-point output and sensitivity of the all-diamond pressure sensor at different calibration temperatures are calculated. The relationship between the zero-point output and sensitivity and temperature is then fitted with a quadratic polynomial to obtain the zero-point temperature drift fitting coefficient and the sensitivity temperature fitting coefficient.

[0023] Specifically, in actual operation, the output voltage of the Wheatstone bridge in an all-diamond pressure sensor can be approximately expressed as the sum of the zero-point voltage and the sensitivity voltage. The zero-point output refers to the non-zero output voltage generated by the bridge when the applied external pressure is zero kPa, due to slight deviations in the initial resistance values ​​of the four piezoresistors (I) in the Wheatstone bridge or asymmetric resistance drift caused by temperature. Sensitivity, on the other hand, refers to the ratio of the change in output voltage to the change in applied pressure. Its physical essence is the amplification factor of the rate of change of the sensor bridge resistance per unit pressure, directly reflecting the efficiency of the sensor's electromechanical conversion.

[0024] During data processing, the output voltage values ​​corresponding to a standard pressure of 0 kPa at each calibrated temperature point are extracted, and these voltage values ​​are used as the zero-point output at each calibrated temperature. A quadratic polynomial equation is constructed to express the zero-point output as a function of temperature. Specifically, the zero-point voltage equals the coefficient of the quadratic term of the zero-point temperature multiplied by the square of the temperature, plus the coefficient of the linear term of the zero-point temperature multiplied by the temperature, plus a zero-point constant term. Using the measured zero-point voltage data at each temperature point, a regression algorithm is employed to fit this quadratic polynomial equation, thereby calculating the corresponding coefficients. These fitting coefficients constitute the zero-point temperature drift fitting coefficients.

[0025] Similarly, the slope of the output voltage change with pressure at each calibration temperature is extracted as the sensitivity at that temperature. The specific sensitivity calculation method is as follows: at a fixed calibration temperature, a linear fit is performed on the 18 output voltages corresponding to the 18 applied standard pressure points. The slope of this linear fit curve is the measured sensitivity value at that temperature. After obtaining the measured sensitivity values ​​at all calibration temperatures, a quadratic polynomial equation for the sensitivity change with temperature is constructed. Specifically, the form of this equation is: sensitivity equals the coefficient of the quadratic term of the sensitivity temperature multiplied by the square of the temperature, plus the coefficient of the linear term of the sensitivity temperature multiplied by the temperature, plus a sensitivity constant term. Using the sensitivity data obtained at each calibration temperature, a regression algorithm is used to fit the parameters of the above equation, thereby solving for the corresponding coefficients. These fitting coefficients constitute the sensitivity temperature fitting coefficients. Compared to higher-order fitting, quadratic polynomial fitting not only reflects the nonlinear and gradual change in the diamond piezoresistive coefficient with temperature but also significantly reduces computational complexity and avoids oscillations caused by polynomial overfitting.

[0026] The zero-point temperature drift fitting coefficient and the sensitivity temperature fitting coefficient are stored in the signal processing chip. The signal processing chip is then used to perform real-time temperature compensation on the original electrical signal of the Wheatstone bridge based on the first correspondence, the zero-point temperature drift fitting coefficient, and the sensitivity temperature fitting coefficient. The temperature drift error is then deducted, and the dynamically compensated pressure value is output.

[0027] Specifically, the signal processing chip can be a microcontroller, digital signal processor, or application-specific integrated circuit integrated into the back end of the pressure sensor or inside its package. When the all-diamond pressure sensor is subjected to actual pressure testing under harsh high-temperature conditions, the signal processing chip reads the resistance change of the on-chip temperature sensor 5 in real time and in situ, and quickly calculates the true real-time temperature of the micro-region thermal field where the sensor is located based on a pre-stored first correspondence. The signal processing chip then substitutes this real-time temperature into a pre-stored zero-point output quadratic polynomial equation to calculate the theoretical zero-point temperature drift value at the current temperature; simultaneously, it substitutes the real-time temperature into a pre-stored sensitivity quadratic polynomial equation to calculate the theoretical actual sensitivity at the current temperature. The signal processing chip reads the original electrical signal output from the Wheatstone bridge led out by the metal interconnect and pad 2, that is, the uncompensated original voltage value. First, it subtracts the calculated theoretical zero-point temperature drift value to deduct the DC component error caused by the zero-point temperature drift. Then, it divides the difference after subtraction by the calculated theoretical actual sensitivity, thereby realizing dynamic gain correction of sensitivity decay with temperature, and finally eliminating the first-order temperature drift error, demodulating and outputting the dynamically compensated pressure value with high precision.

[0028] By employing the aforementioned on-chip in-situ temperature measurement based on a completely consistent physical thermal field, and a decoupling compensation method based on calibration testing and quadratic polynomial fitting, the spontaneous temperature drift of the all-diamond varistor caused by temperature can be accurately reduced. Within the full-range pressure range, the high-temperature drift of the sensor under high-temperature conditions can be controlled to an extremely low level. In essence, this embodiment can control it to within 0.02 percent of full scale per degree Celsius, completely overcoming the bottlenecks of thermal hysteresis and inaccurate compensation caused by packaging stress interference in heterogeneous external temperature sensors. This fully leverages the advantages of diamond materials in high-temperature resistance and high-precision pressure measurement under extreme high-temperature conditions.

[0029] Example 2 Based on the aforementioned embodiments, this embodiment designs the physical structure, spatial layout, and materials science configuration of the all-diamond pressure sensor to maximize the solution at the hardware level to the bottleneck problems of minimal diaphragm deformation, stress dispersion, and low detection sensitivity caused by the ultra-high hardness and high elastic modulus of the all-diamond pressure sensor.

[0030] like Figure 2 As shown, this embodiment provides an all-diamond pressure sensor, the basic carrier of which is a single-crystal diamond substrate. The back and front sides of the single-crystal diamond substrate are micro-machined and etched to form a beam-island-film composite structure sensitive diaphragm, namely the diamond sensitive film 7. The beam-island-film composite structure sensitive diaphragm, namely the diamond sensitive film 7, is composed of a central rigid mass island 3, four-way square cantilever beams 6 distributed in a cross-shaped symmetrical pattern, and surrounding fixed support areas 4, namely the surrounding stress-free areas, disposed on the outside of the square cantilever beams 6.

[0031] Specifically, in order to generate more concentrated local bending stress under the same pressure load, the diaphragm abandons the traditional uniform thickness flat-bottom diaphragm design and instead adopts a highly complex beam-island-membrane composite three-dimensional design. The overall dimensions of the single-crystal diamond diaphragm are designed to be 800 micrometers in length and 800 micrometers in width, and the thickness of the diaphragm, which is the substrate thickness of the diamond sensitive film 7, is 20 micrometers.

[0032] The central rigid mass island 3, located at the center of the diaphragm, is designed with dimensions of 200 micrometers in length, 200 micrometers in width, and 50 micrometers in thickness. The thickness of this central rigid mass island 3 is significantly greater than that of the surrounding diaphragm, and under full-scale pressure load, the central rigid mass island 3 itself undergoes almost no elastic deformation. Due to its extremely high rigidity, the central rigid mass island 3 can suppress excessive deformation in the central region of the diaphragm, forcibly transferring and redistributing the pressure load uniformly applied externally to the surface of the diamond-sensitive film 7 to the surrounding, less stiff square cantilever beam 6 region, thus achieving the first stage of stress concentration.

[0033] Four square cantilever beams 6 are arranged in a cross-shaped symmetrical pattern. Each square cantilever beam 6 is designed with a length of 300 micrometers, a width of 40 micrometers, and a thickness of 30 micrometers. One end of the square cantilever beam 6 is rigidly integrated with the central rigid mass island 3, and the other end is connected to the surrounding fixed support area 4 around the single-crystal diamond diaphragm. Due to the aspect ratio of the square cantilever beam 6 reaching 7.5, it has optimal bending freedom and mechanical stability, and can produce local bending deformation when subjected to stress transmitted from the central rigid mass island 3. Through this precise beam size constraint, pressure can generate a severe and concentrated bending stress peak at the root of the square cantilever beam 6, that is, at the junction area connected with the surrounding fixed support area 4. The local stress intensity can reach three to five times that of a traditional flat-bottomed diaphragm of the same thickness, realizing the second stage amplification of stress, while ensuring the uniformity of stress distribution at the root of the square cantilever beam 6, so that the sensor as a whole has excellent measurement linearity.

[0034] The perimeter support area 4, located outside the square cantilever beam 6, is a physically zero-stress region extending outward from the perimeter support area of ​​the diaphragm. When the sensor is subjected to full-scale external pressure load, this region experiences minimal mechanical stress due to its distance from the main bending deformation of the square cantilever beam 6 and its protection by the rigid outer frame; it is almost unaffected by mechanical deformation stress. This provides a natural physical decoupling environment for the integration of the temperature sensor 5, avoiding piezoresistive interference caused by mechanical deformation, and significantly improving the purity and accuracy of temperature measurement.

[0035] In this embodiment, multiple boron-doped diamond varistors 1 are grown in situ and etched into the maximum principal stress concentration region at the root of the square cantilever beam 6. Specifically, four boron-doped diamond varistors 1 are used, each shaped as a narrow strip. The long axes of these four boron-doped diamond varistors 1 are all arranged along the -1-0 crystal orientation of the single-crystal diamond substrate. The -1-0 crystal orientation is chosen because, in the cubic diamond crystal system, the piezoresistive coefficient of boron-doped diamond in the -1-0 crystal orientation is the largest among all crystal orientations, approximately 1.5 to 2 times that of other conventional crystal orientations. By aligning the long axes of the four varistors 1 with the -1-0 crystal orientation, the electromechanical conversion efficiency of the diamond can reach its theoretical maximum value. Four diamond varistors 1 are interconnected through on-chip metal interconnects and pads 2 to form a closed-loop Wheatstone bridge. Two varistors 1 on the roots of the two opposing square cantilever beams 6 experience tensile stress when compressed, resulting in an increase in resistance. The other two varistors 1 on the roots of the two opposing square cantilever beams 6 experience compressive stress when compressed, resulting in a decrease in resistance. Through the differential amplification effect of the bridge, the small resistance change is converted into a highly sensitive differential voltage output.

[0036] The on-chip temperature sensor 5, also known as the on-chip platinum resistance temperature sensor, employs a high-sensitivity, low-heat-capacity serpentine structure design, integrated within the surrounding fixed-support region 4. Because this temperature sensor 5, along with the boron-doped diamond varistor 1 and the single-crystal diamond substrate, are in-situ homogeneously integrated, they reside within the same extremely small micro-thermal field, with a linear distance of only a few hundred micrometers between them. Therefore, their thermal inertia exhibits high consistency. Even under drastic fluctuations in ambient temperature, the temperature sensor 5 can acquire the actual operating temperatures of the single-crystal diamond substrate and the varistor 1 with zero hysteresis and extreme accuracy.

[0037] The metal interconnects and pads 2, i.e., the metal electrode layer, are disposed on the single-crystal diamond substrate, forming stable ohmic contact connections with four boron-doped diamond varistors 1 and the on-chip temperature sensor 5, respectively. The metal interconnects and pads 2 are used to extract the raw electrical signal of the Wheatstone bridge and the real-time resistance change signal of the on-chip temperature sensor 5 to the external signal processing chip without loss and with high signal-to-noise ratio, providing the most original and high-quality physical data for dynamic temperature decoupling compensation.

[0038] Example 3 like Figure 3As shown, this embodiment describes the specific fabrication method of the all-diamond pressure sensor based on the aforementioned embodiments. Due to the extremely high hardness and chemical stability of the all-diamond material, the microfabrication process for all-diamond sensors is exponentially more difficult than that for traditional silicon-based devices. This embodiment optimizes the process timing, adopting a method of first epitaxially growing a doped thin film and then etching to define the resistance. Combined with high-precision crystal orientation alignment, the controllability of the piezoresistive crystal orientation is achieved. Furthermore, the fabrication challenge of the beam-island-film composite structure is overcome by employing ultrashort pulse femtosecond laser double-sided etching. The specific process consists of steps 1 to 5, detailed as follows: Step 1: Substrate pretreatment and in-situ growth of piezoresistive sensitive layer.

[0039] In this embodiment, a high-purity electronic-grade single-crystal diamond substrate was selected. The front surface of the substrate was a (100) crystal plane with extremely low roughness. The substrate was placed in a standard ultrasonic cleaning tank and subjected to a standard organic cleaning process, including acetone washing, anhydrous ethanol washing, and deionized water washing, to remove organic impurities adhering to the surface. The substrate was then immersed in a hot mixed strong acid solution of concentrated sulfuric acid and nitric acid for inorganic cleaning to thoroughly remove trace metal ions and inorganic dirt remaining on the diamond surface.

[0040] After cleaning, the single-crystal diamond substrate is placed in a microwave plasma chemical vapor deposition (PCVDC) reaction chamber. High-purity hydrogen and methane are used as the reaction precursor gases, while gaseous diborane is introduced as the dopant source. High-temperature hydrogen plasma is generated within the reaction chamber via microwave excitation. Under the influence of the plasma, a high-quality boron-doped single-crystal diamond film is epitaxially grown in situ on the front side of the single-crystal diamond substrate. The growth and doping are completed simultaneously in one step, ensuring perfect lattice matching between the epitaxial film and the substrate single-crystal diamond, and extremely uniform spatial distribution of boron atoms within the lattice. The resulting boron-doped diamond film serves as the subsequent piezoresistive sensing layer, with its thickness precisely controlled at 3 micrometers and the boron doping concentration precisely controlled at 3 x 10¹⁸ centimeters per cubic centimeter. At this thickness and doping concentration, the diamond film exhibits both optimal piezoresistive sensitivity and excellent conductivity.

[0041] Step 2: Fabrication of varistors and Wheatstone bridges.

[0042] Because the piezoresistive effect of boron-doped diamond thin films exhibits strong anisotropy, in order to ensure that the fabricated piezoresistor 1 operates in the direction of maximum piezoresistive force, this embodiment utilizes electron backscattering diffraction technology to perform precise crystal orientation testing on the epitaxially grown piezoresistive sensitive layer, accurately determining the specific crystallographic orientation of the thin film within the horizontal plane of its surface. Based on the measured crystal orientation, when designing the photolithography mask layout, the long, narrow geometrical side of the piezoresistor 1 is precisely aligned and coincides with the -1-0 crystal orientation of the thin film.

[0043] A high-resolution photoresist resistant to dry etching is uniformly spin-coated onto the surface of the piezoresistive sensitive layer. High-precision alignment, exposure, development, and fixing are then performed using a double-sided lithography machine to align the four designed edges. <110> The pattern of the varistor 1 with a cross-shaped symmetrical crystal orientation and the connecting lines is transferred onto the photoresist.

[0044] The substrate was placed in the cavity of an inductively coupled plasma dry etching machine. High-purity oxygen and argon were introduced as etching gases, and a high-power radio frequency generator was set to excite high-density oxygen-containing plasma. A physicochemical dual anisotropic etching process was performed on the boron-doped diamond film not covered by photoresist. The etching depth was set to 3 micrometers to ensure complete penetration of the epitaxial boron-doped film and exposure of the underlying intrinsic single-crystal diamond substrate, thereby completely isolating four isolated, symmetrically distributed 1-0 crystal orientation boron-doped diamond varistors. After etching, residual photoresist on the surface was thoroughly removed using a strong acetone solution and deoxygenated plasma ashing process, followed by ultrasonic cleaning.

[0045] Step 3: Laser micro-etching of the beam-island-membrane composite structure.

[0046] Because single-crystal diamond has a Mohs hardness of 10 and extremely high chemical inertness, traditional chemical etching or conventional dry etching methods are insufficient for etching complex three-dimensional structures with high aspect ratios reaching depths of tens of micrometers. To overcome this challenge, this embodiment employs an ultrashort pulse femtosecond laser to perform high-precision selective three-dimensional laser ablation etching on both the front and back sides of the single-crystal diamond substrate.

[0047] Specifically, femtosecond lasers possess extremely high peak power and extremely short pulse widths, enabling energy to be concentrated in extremely small micro-areas within nanosecond timescales. This allows diamond materials to directly sublimate and vaporize, achieving cold processing with virtually no heat-affected zone. During the etching process, a high-precision multi-axis CNC translation stage controls the scanning path of the laser beam. The laser scans the front side to define the outline of the square cantilever beam 6, and scans the back side to remove large volumes of diamond material, defining the back cavity and the central rigid mass island 3. During etching, an online spectral thickness gauge and an infrared displacement sensor are used to monitor the etching depth and residual film thickness in real time. This ensures the precise formation of a complex composite film structure consisting of the central rigid mass island 3, the square cantilever beam 6, and the surrounding fixed support area 4 (i.e., a stress-free area), guaranteeing that the film thickness uniformity error of the entire batch of devices is controlled within ±1 micrometer.

[0048] After laser etching, the diamond surface develops a trace carbonized recast layer and micro-mechanical cracks due to localized micro-heating. The substrate is then boiled in concentrated sulfuric acid to remove the carbon deposits, followed by a slight chemical mechanical polishing (CMP). This CMP uses a nano-scale silica polishing slurry to lightly grind both sides of the film, removing surface micro-cracks and high-frequency roughness caused by laser impact. This achieves a nano-scale mirror finish on the film surface, significantly eliminating stress concentration points on the diamond sensitive film 7 under long-term alternating pressure bending, preventing the initiation of fatigue cracks, and significantly improving the long-term mechanical stability and mechanical fatigue life of the sensitive film.

[0049] Step 4: On-chip integration of metal electrodes and temperature sensor.

[0050] On the cleaned and polished substrate surface, three continuous metal thin films of titanium, platinum, and gold are sequentially deposited using electron beam evaporation or magnetron sputtering to serve as the metal interconnects and pads 2 of the Wheatstone bridge. The bottom titanium layer is 100 nm thick, the middle platinum barrier layer is 100 nm thick, and the top gold bonding contact layer is 200 nm thick. After deposition, the three metal layers are patterned using standard metal lift-off photolithography or wet etching to form interconnect electrodes that attach to the two ends of the four varistors 1.

[0051] In this embodiment, to form a stable, high-quality contact between titanium and single-crystal diamond, the chip is placed in a tubular annealing furnace, and annealed at 400 degrees Celsius for one hour using an inert protective gas such as high-purity nitrogen or argon. Under this high-temperature annealing, the titanium atoms at the bottom undergo a localized solid-phase chemical reaction with the carbon atoms on the diamond surface, forming an extremely thin and uniform titanium carbide transition layer in situ. This titanium carbide transition layer not only significantly reduces the contact resistance between titanium and diamond to below 10⁻⁵ ohms per square centimeter, forming a perfect ohmic contact, but also locks the metal atoms in place, greatly preventing interdiffusion and detachment of the metal under high-temperature operating conditions, thus ensuring the long-term electrical stability of the sensor under extreme high-temperature conditions above 500 degrees Celsius.

[0052] In the perimeter support region 4 (stress-free region) of a single-crystal diamond substrate, a high-purity platinum layer is deposited using magnetron sputtering, with a film thickness controlled at 500 nanometers. A high aspect ratio serpentine platinum resistor pattern is defined on the platinum layer surface using fine photolithography, and wet etching is performed using a dedicated metal etching solution to form the serpentine on-chip temperature sensor 5. In this process, to avoid direct trace electrochemical interaction between the high-purity platinum and the underlying diamond, preferably, before depositing the platinum layer, a 100-nanometer-thick silicon dioxide insulating layer is first deposited on the single-crystal diamond surface in the perimeter support region 4 using plasma-enhanced chemical vapor deposition. Then, the serpentine platinum resistor is fabricated on the silicon dioxide insulating layer, thereby achieving complete physical and electrical insulation between the temperature sensor 5 and the diamond substrate, eliminating leakage current interference.

[0053] Step 5: High-temperature hermetic sealing.

[0054] After fabricating the metal interconnects and pads 2 on the chip surface and the temperature sensor 5, a high-temperature resistant alumina ceramic socket is used as the physical support shell for the sensor. Gold-tin alloy solder is filled between the bonding surfaces of the chip back and the alumina ceramic socket, and high-temperature eutectic bonding is performed under nitrogen atmosphere protection to achieve a robust and integrated support between the chip and the socket. Using an automatic bonding machine, high-purity gold wire is used to bond the electrodes of the various metal interconnects and pads 2 on the chip surface to the external metal leads of the socket. In a vacuum chamber, laser resistance welding or high-temperature ceramic adhesive sealing is used to complete the vacuum or inert gas hermetic encapsulation of the entire sensor, ultimately resulting in an integrated temperature-compensated all-diamond piezoresistive pressure sensor that can be directly applied to extreme operating conditions.

[0055] The all-diamond pressure sensor fabricated in this embodiment has a compact overall structure and tiny physical dimensions. By completely abandoning traditional silicon-based or metal substrates, it eliminates thermal stress failure caused by the mismatch in thermal expansion coefficients of heterogeneous materials. Simultaneously, in conjunction with the on-chip in-situ temperature sensor 5 and the aforementioned temperature-pressure decoupling compensation method, this sensor can output high-precision pressure monitoring data stably and without distortion under extreme conditions such as high temperatures up to 500 degrees Celsius, pressures up to 170 kPa, and strong corrosion. It possesses extremely high industrial application and engineering promotion value.

[0056] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A dynamic temperature compensation method for an all-diamond pressure sensor, characterized in that, include: Temperature characteristics of the on-chip platinum resistance temperature sensor of the all-diamond pressure sensor are calibrated. Based on the calibration data, the first correspondence between the real-time temperature and the resistance value of the on-chip platinum resistance temperature sensor is obtained by least squares fitting. At different calibration temperature points, standard pressures of different gradients were applied to the all-diamond pressure sensor, and the output voltage of the Wheatstone bridge in the all-diamond pressure sensor was measured. Based on the output voltage, the zero-point output and sensitivity of the all-diamond pressure sensor at different calibration temperatures were calculated, and the relationship between the zero-point output and sensitivity and temperature was fitted by a quadratic polynomial to obtain the zero-point temperature drift fitting coefficient and the sensitivity temperature fitting coefficient. The zero-point temperature drift fitting coefficient and the sensitivity temperature fitting coefficient are stored in the signal processing chip. The signal processing chip is then used to perform real-time temperature compensation on the original electrical signal of the Wheatstone bridge based on the first correspondence, the zero-point temperature drift fitting coefficient, and the sensitivity temperature fitting coefficient. The temperature drift error is then deducted, and the dynamically compensated pressure value is output.

2. The dynamic temperature compensation method for the all-diamond pressure sensor according to claim 1, characterized in that, Temperature characteristic calibration of the on-chip platinum resistance temperature sensor for the all-diamond pressure sensor, including: Multiple uniformly distributed temperature points were selected within the range of 25℃ to 500℃; At each temperature point, maintain the temperature for a preset time. After thermal equilibrium is reached, measure the resistance value of the on-chip platinum resistance temperature sensor.

3. The dynamic temperature compensation method for the all-diamond pressure sensor according to claim 2, characterized in that, There are 10 temperature points evenly distributed across the entire temperature range, with a preset time of 30 minutes.

4. The dynamic temperature compensation method for the all-diamond pressure sensor according to claim 1, characterized in that, At different calibration temperature points, standard pressures of different gradients were applied to the all-diamond pressure sensor, including: At each calibrated temperature point, multiple standard pressure points within the full-scale range of 0 kPa to 170 kPa were applied to the all-diamond pressure sensor. The output voltage of the Wheatstone bridge at various standard pressure points was collected.

5. The dynamic temperature compensation method for the all-diamond pressure sensor according to claim 4, characterized in that, There are 18 standard pressure points.

6. The dynamic temperature compensation method for the all-diamond pressure sensor according to claim 1, characterized in that, The relationships between zero-point output and sensitivity with temperature were fitted using a quadratic polynomial, including: The output voltage at each calibrated temperature point with a standard pressure of 0 kPa is extracted as the zero-point output. A quadratic polynomial equation for the zero-point output as a function of temperature is constructed and fitted to obtain the zero-point temperature drift fitting coefficient. The slope of the output voltage change with pressure at each calibration temperature point is extracted as the sensitivity. A quadratic polynomial equation of the sensitivity change with temperature is constructed and fitted to obtain the sensitivity temperature fitting coefficient.

7. The dynamic temperature compensation method for the all-diamond pressure sensor according to claim 1, characterized in that, Real-time temperature compensation keeps the temperature drift of the all-diamond pressure sensor within 0.02% FS / ℃ across the entire pressure range.

8. A full diamond pressure sensor, characterized in that, include: A single-crystal diamond substrate is used. The back and front sides of the single-crystal diamond substrate are etched to form a beam-island-film composite structure sensitive film. The beam-island-film composite structure sensitive film includes a central rigid island, four-way support beams distributed in a cross-shaped symmetrical manner, and a stress-free area around the four-way support beams. Multiple boron-doped diamond varistors were grown in situ and etched into the region of maximum principal stress concentration at the root of a four-way support beam, with the long axis of each boron-doped diamond varistor aligned along the single-crystal diamond substrate. <110> Crystal orientations are interconnected to form a Wheatstone bridge; The on-chip platinum resistance temperature sensor adopts a serpentine structure design and is integrated in the stress-free area around it for in-situ acquisition of the real-time temperature of a single-crystal diamond substrate. The metal electrode layer is electrically connected to the boron-doped diamond varistor and the on-chip platinum resistance temperature sensor.

9. A method for fabricating an all-diamond pressure sensor, characterized in that, include: A single-crystal diamond substrate was selected, and a boron-doped diamond film was grown in situ on its front side using microwave plasma chemical vapor deposition as a piezoresistive sensitive layer. The crystal orientation of the piezoresistive sensitive layer was determined by electron backscatter diffraction. Based on the measured crystal orientation, a layer was formed along the crystal orientation using photolithography and inductively coupled plasma dry etching. <110> Four boron-doped diamond varistors with symmetrical crystal orientation are interconnected to form a Wheatstone bridge. Using an ultrashort pulse femtosecond laser, selective etching is performed on the back and front sides of a single-crystal diamond substrate to precisely form a central rigid island, a four-way support beam, and a stress-free area around the perimeter, resulting in a beam-island-film composite structure sensitive film. A Ti / Pt / Au three-layer metal was deposited on the piezoresistive sensitive layer and patterned to form the interconnects and lead-out electrodes of the Wheatstone bridge. The layer was then annealed in an inert atmosphere at 400°C to generate a stable TiC transition layer at the Ti-diamond interface. A high-purity platinum layer is deposited in the stress-free area around the chip and photolithographically formed into a serpentine platinum resistor, which serves as an on-chip platinum resistance temperature sensor.

10. The method for preparing the all-diamond pressure sensor according to claim 9, characterized in that, The overall dimensions of the single-crystal diamond substrate are 800μm × 800μm, and the thickness is 20μm; The central rigid island has dimensions of 200μm × 200μm and a thickness of 50μm; Each four-way support beam measures 300μm in length, 40μm in width, and 30μm in thickness.

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