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## Creator

Zilong Zhang, Keyun Gu, Guo Chen, [Yasuo Koide](https://orcid.org/0000-0001-8321-9822), [Satoshi Koizumi](https://orcid.org/0000-0003-4961-5658), [Meiyong Liao](https://orcid.org/0000-0003-1361-4266)

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[Diamond NEMS Resonators for Real-Time Dual Sensing of Magnetic Fields and Temperatures up to 500°C](https://mdr.nims.go.jp/datasets/54704e7f-c535-492b-840f-d3db0bddb883)

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Paper Title (use style: paper title)Diamond NEMS Resonators for Real-Time Dual Sensing of Magenitc Fields and Temperatures up to 500℃Zilong Zhang, Keyun Gu, Guo Chen, Yasuo Koide, Satoshi Koizumi and Meiyong LiaoEmail: meiyong.liao@nims.go.jpNational Institute for Materials Science (NIMS), Tsukuba, JAPANAbstract—Real-time multifunctional sensing of magnetic fields and temperatures with preserved performances from room temperature to 500℃ has posed a challenge for conventional sensing techniques. In this work, we demonstrate a new and smart multifunctional sensor based on single crystal diamond (SCD) NEMS resonators that can sense both magnetic fields and temperatures up to 500℃. Our strategy is to integrate a magnetostrictive thin film (Curie temperature >650℃) and a non-magnetic thin film on different SCD NEMS resonators on the same SCD chip for magnetic field sensing and temperature sensing, respectively. The multifunctional SCD NEMS sensor can achieve simultaneous sensing of temperatures and magnetic fields with high reliability up to 500℃, the best among all the semiconductors. The concept of SCD-NEMS based multifunctional sensors offers a promising solution for developing multifunctional sensors of magnetic sensing and temperature sensing under harsh environments.Keywords—Single crystal diamond, NEMS resonator, magnetic sensing, temperature monitoringI. IntroductionMultifunctional sensors are essential in diverse applications that require the sensing of multiple physical, chemical, and environmental parameters within a highly integrated system, as well as in the context of miniaturization and the Internet of Things (IoT). At present, multifunctional sensors encounter the contradiction of functional diversity and cost increase, fabrication limitation [1-5] ADDIN EN.CITE . Particularly, the real-time multifunctional sensing of magnetic field and high temperature up to 500℃ has not been achieved. Single-crystal diamond (SCD) offers great potential as a material for developing high-performance and highly reliable NEMS devices owing to its exceptional electrical properties, mechanical strength, and chemical inertness [6-10] ADDIN EN.CITE . Galfenol (FeGa) demonstrates a significant magneto-strictive coefficient and outstanding thermal stability, boasting an ultra-high Curie temperature of 675°C [11]. In addition, tungsten carbide (WC) film has advantages of high thermal-stability and high oxidation resistance, which makes it promising for temperature sensing in wide temperature range. The combination of SCD with FeGa film and WC film in NEMS technology harnesses the strengths of these materials, resulting in high sensitivity and reliability devices at high temperatures.In this work, we demonstrate the dual functional sensors for magnetic fields and temperatures up to 500oC by using different SCD NEMS resonators integrated with a FeGa/Ti film and a WC/Ti film separately to overcome the challenge of conventional sensors with poor thermal stability and reliabilityII. Device ConceptThe device configuration of the SCD-based multifunctional sensors consist of two SCD NEMS resonators coupling with a WC/Ti layer and a FeGa/Ti layer, respectively, as shown in Fig. 1(a). The FeGa/Ti/SCD resonator sensor is proposed to realize magnetic sensing. Simultaneously, the ambient temperature is monitored and detected by the WC/Ti/SCD resonator sensor. The magnetic sensing principle is based on magnetostictive effect (∆E effect). The magnetic sensitivity is defined as the resonance frequency shift upon the magnetic field. The Young’s modulus of the FeGa/Ti/SCD structure is changed under applying magnetic field, which results in the resonance frequency shift. The resonance frequency shift, ∆fH, generated by applying magnetic field can be expressed as,∆fH=fH-f0=0.162*t(EH1/2-E01/2)/(L2ρ1/2)(1)wherein t and L are the thickness and length of the cantilever. EH and E0 are the Young’s modulus with and without applying the magnetic field, respectively. fH and f0 represent the resonance frequencies with and without applying the magnetic field. The larger ∆E effect can achieve enhanced magnetic sensing performance. The thermal expansion mismatch of the WC/Ti film and SCD resonator is utilized to realize the temperature sensing. The temperature sensitivity is characterized as the resonance frequency shift upon the temperature increasing. The resonance frequency shift, ∆fT, resulted from the temperature variation is described,∆fT=fT-fT0=0.162*t(ET1/2-ET01/2)/(L2ρ1/2)(2)where ET and ET0 are the Young’s modulus at the temperature of T and 25℃, respectively. fT and fT0 represent the resonance frequencies at the temperature of T and 25℃. The high thermal expansion mismatch is in favor of obtaining large Young’s modulus change of the WC/Ti/SCD structure, in return achieving high temperature sensing performance.III. Device Fabrication and MeasurementIn this work, the smart-cut technique is employed to produce the SCD resonators  ADDIN EN.CITE [12-14]. After the releasing, the as-fabricated SCD cantilevers were annealed at 650°C for 10 hrs in a tube furnace with an oxygen ambient to improve the Q factors. The FeGa film, WC film, and Ti film were deposited on the SCD cantilever by the radio frequency magnetron sputtering. The Ti interlayer was used to improve the adhesion amongst the multilayer structures. An optical system based on Doppler effect of a focused laser (He-Ne laser, 633 nm, <1mW) incident vertically on the substrate was utilized to measure the out-of-plane resonance frequencies of the SCD-based resonators, as shown in Fig. 1(b). The lock-in amplifier system was used to read out the resonance signal. All measurements were conducted in a vacuum chamber with a pressure below 10-3 Pa. The resonators were actuated by utilizing a micro-probe connected to an RF range signal. The magnetic fields, resulted from different magnets, perpendicular to the resonator in the same plane were applied for magnetic sensing measurements.IV. Results And DiscussionA. High thermal-stability of the SCD NEMS resonatorsFig. 1(c) exhibits the resonance frequency spectrum shifts downward with the etching duration increasing, which is due to the reduction of the thickness in the etching process. The Q factors of the SCD cantilevers are greatly enhanced from 15551.3 to 95539.4 by the etching treatment (Fig. 1(d)). The high Q factor contributes to achieving high-sensitivity 902.8903.0903.2903.4 2 V 4 V 6 V 8 V 10 V  Amplitude (a.u.)Frequency (kHz)With WC/Ti filmL=120 mm@25°C896.8897.6898.4899.2900.0   2 V 4 V 6 V 8 V 10 VAmplitude (a.u.)Frequency (kHz)With WC/Ti filmL=120 mm@500°C246810L=120 mm 25°C 500°C Linear fitting Linear fitting  Ampl. peak (a.u.)Voltage (V)897 898 89990090190290325℃500℃ Amplitude (a.u.)Frequency (kHz)With WC/Ti film, L=120 mm0100200 300 400 500-5-4-3-2-101With WC/Ti filmL=120 mm Linear fitting  Frequency shift (kHz)Temperature (°C)10.1 Hz/°C010020030040050001020  Q factor (103)Temperature (°C)With WC/Ti filmL=120 mm(a) (b) (c)(d) (e) (f)and low-noise sensors. The dependences of the resonance frequencies and the Q factors on the lengths of the SCD cantilevers after the etching treatment are depicted in Fig. 1(e) and (f). The rule of resonance frequencies and lengths of the SCD cantilevers strictly follows the law of (1). After the etching treatments, the Q factor exhibits the positive-451.6451.7451.8   2 V 4 V 6 V 8 V 10 VAmplitude (a.u.)Frequency (kHz)With FeGa/Ti filmL=160 mm@25°C448.5449.0449.5   2 V 4 V 6 V 8 V 10 VAmplitude (a.u.)Frequency (kHz)With FeGa/Ti film=160 mm@500°C246810L=160 mm 25°C 500°C Linear fitting Linear fitting  Ampl. peak (a.u.)Voltage (V)449.0 449.5 450.0450.5451.0451.5  Amplitude (a.u.)Frequency (kHz)With FeGa/Ti film, L=160 mm25°CSolid line:without magnetDash line:with magnet500°C012 3 45-1001020   25°C 100°C 200°C 300°C 400°C 500°CFrequency shift (Hz)Magnetic field (mT)With FeGa/Ti filmL=160 mm0100200300400500510152025L= 160 mmH= 4.73 mT   Without magnet With magnetQ (103)Temperature (°C)(a) (b) (c)(d)(e)(f)dependence on the length, which indicates that the Q factor is mainly determined by the clamping loss dissipation.Fig. 2(a) shows the resonance spectrum of a SCD cantilever shifts downward with the evaluated temperature increasing. The dependence of the resonance frequency of the SCD cantilever (L=120 μm) as the measurement temperature during the heating and cooling process is shown in Fig. 2(b). It is shown that the resonance frequency is almost identical for the temperature during the heating and cooling process, which indicates the high thermal stability of the SCD cantilevers. The thermal stability of the SCD resonator is also confirmed by the Q factor variations of the SCD cantilever with temperature during heating and cooling processes (Fig. 2(c)). Based on equation (2), the temperature coefficient of resonance frequency (TCF), namely, TCF=(∆fT/f0)/∆T, was utilized to reveal the thermal stability of the SCD cantilever. The TCF of the SCD cantilever shows weak temperature-dependence of a value of 7.8 ppm/℃ (Fig. 2(d)), which ensures the SCD cantilever as the thermally-stable platform for functional sensorsB. Temperature sensingThe coupling of SCD cantilever with the WC/Ti film offers a promising device configuration to realize the temperature sensing. This is attributed to 1) the existence of the thermal expansion between the SCD and the WC/Ti film, 2) the ultra-high thermal stability of the SCD and the WC/Ti. Fig. 3(a) and (b) show the dependence of the resonance spectrum of a WC/Ti/SCD sensor (L=120 μm) on the actuation voltage at 25℃ and 500℃. The temperature sensor exhibits good resonance vibration features at different voltages. The amplitude peaks of the resonance spectra linearly increase with the driving voltages (Fig. 3(c)). It indicates that the resonance frequency of the sensor shows no dependence on the actuation voltage. Fig. 3(d) shows the dependence of the resonance frequency of the WC/Ti/SCD sensor on the measurement temperature. The WC/Ti/SCD sensor can reach a high temperature sensitivity of 10.1 Hz/℃ within the wide temperature range of 25℃~500℃ (Fig. 3(e)). The trend of Q factor of the temperature sensor shows a negative temperature-dependence (Fig. 3(f)).C. Magnetic sensingThe magnetic sensor is based on the FeGa/Ti/SCD structure. When the response of the WC/Ti/SCD sensor to the temperature is achieved, the magnetic sensing of the FeGa/Ti/SCD sensor is simultaneously obtained. Fig. 4(a) and (b) show the dependence of the resonance spectra of a FeGa/Ti/SCD sensor (L=160 μm) on the actuation voltage without applying magnetic fields, exhibiting good resonance vibration features at different voltages. The amplitude peaks of the resonance spectra also linearly increase with the driving voltages (Fig. 4(c)). Fig. 4(d) schematically shows the resonance frequency shift of the magnetic sensor without and with a magnetic field (H=4.73 mT) at different measurement temperatures. Fig. 4(e) shows the dependence of the resonance frequency shifts upon the magnetic fields at different measurement temperatures. It is disclosed that the magnetic sensing performance is enhanced with the temperature increasing. This is possibly due to the enhanced strain coupling at the interfaces at high temperatures [4]. The FeGa/Ti/SCD sensor can reach the highest magnetic sensitivity of 4.4 Hz/mT at 500℃ (Fig. 4(e)). The Q factor of the magnetic sensor decreases with the temperature without and with magnetic fields (Fig. 4(f)).V. Conclusion In summary, for the first time the multifunctional sensors for simultaneous realization of temperature sensing and magnetic field sensing based on the SCD-based resonators in wide working temperature range of 25℃~500℃ were demonstrated. The high temperature sensitivity of 10.1 Hz/℃ and high magnetic sensitivity of ~4.4 Hz/mT at 500℃ for the multifunctional sensors with high reliability and wide working temperature range were achieved, exhibiting a great promising for the future sensing applications of high-integration, multifunction, miniaturization.AcknowledgmentThis work was supported by JSPS KAKENHI (No. 20H02212, 22K18957, 15H03999), a Grant-in-Aid for JSPS Research Fellows (No. 22F21341), and Tsukuba Global Innovation Promotion Agency and Nanotechnology Platform projects sponsored by the Ministry of Education, Culture, Sports, and Technology (MEXT) of Japan.References[1]B. Gleich, I. Schmale, T. Nielsen et al., “Miniature magneto-mechanical resonators for wireless tracking and sensing,” Science, vol. 380, no. 6648, pp. 966-971, 2023.[2]S. Hsieh, P. Bhattacharyya, C. Zu et al., “Imaging stress and magnetism at high pressures using a nanoscale quantum sensor,” Science, vol. 366, no. 6471, pp. 1349-1354, 2019.[3]J. Hanna, M. Bteich, Y. Tawk et al., “Noninvasive, wearable, and tunable electromagnetic multisensing system for continuous glucose monitoring, mimicking vasculature anatomy,” Science Advances, vol. 6, no. 24, pp. eaba5320, 2020.[4]N. Zavanelli, H. Kim, J. Kim et al., “At-home wireless monitoring of acute hemodynamic disturbances to detect sleep apnea and sleep stages via a soft sternal patch,” Science advances, vol. 7, no. 52, pp. eabl4146, 2021.[5]Y. Yang, P. Mengue, H. Mishra et al., “Wireless multifunctional surface acoustic wave sensor for magnetic field and temperature monitoring,” Advanced Materials Technologies, vol. 7, no. 3, pp. 2100860, 2022.[6]A. Banerjee, D. Bernoulli, H. Zhang et al., “Ultralarge elastic deformation of nanoscale diamond,” Science, vol. 360, no. 6386, pp. 300-302, 2018.[7]C. Dang, J.-P. Chou, B. Dai et al., “Achieving large uniform tensile elasticity in microfabricated diamond,” Science, vol. 371, no. 6524, pp. 76-78, 2021.[8]O. Auciello, “Science and technology of a transformational multifunctional ultrananocrystalline diamond (UNCDTM) coating,” Functional Diamond, vol. 2, no. 1, pp. 1-24, 2022.[9]Y. Tao, J. M. Boss, B. Moores et al., “Single-crystal diamond nanomechanical resonators with quality factors exceeding one million,” Nature communications, vol. 5, no. 1, pp. 1-8, 2014.[10]E. Sillero, O. A. Williams, V. Lebedev et al., “Static and dynamic determination of the mechanical properties of nanocrystalline diamond micromachined structures,” Journal of micromechanics Microengineering, vol. 19, no. 11, pp. 115016, 2009.[11]T. Ma, J. Gou, S. Hu et al., “Highly thermal-stable ferromagnetism by a natural composite,” Nature communications, vol. 8, no. 1, pp. 13937, 2017.[12]Z. Zhang, H. Wu, L. Sang et al., “Enhancing delta E effect at high temperatures of Galfenol/Ti/single-crystal diamond resonators for magnetic sensing,” ACS applied materials & interfaces, vol. 12, no. 20, pp. 23155-23164, 2020.[13]Z. Zhang, H. Wu, L. Sang et al., “Single-crystal diamond microelectromechanical resonator integrated with a magneto-strictive galfenol film for magnetic sensing,” Carbon, vol. 152, pp. 788-795, 2019.[14]M. Liao, S. Hishita, E. Watanabe et al., “Suspended single‐crystal diamond nanowires for high‐performance nanoelectromechanical switches,” Advanced Materials, vol. 22, no. 47, pp. 5393-5397, 2010.�Fig. 1. (a) Optical image of the multifunctional sensors. (b) Schematic measurement setup of the multifunctional sensor based on a SCD resonator. (c) Resonance spectrum shift with the etching treatment. (d) Q factor variations before and after the etching treatment. Dependences of (e) resonance frequency and (f) Q factor on length of SCD resonators after the etching treatment.�Fig. 2. (a) Resonance spectra shifts of a bare SCD cantilever as a function of the measurement temperature. Dependences of (b) the resonance frequency and (c) Q factor of the SCD cantilever (L=120 μm) as the measurement temperature during the heating and cooling process. (d) Dependence of the ratio of frequency shift to the resonance frequency of the bare SCD cantilever on the temperature.�Fig. 3. Resonance spectra of the WC/Ti/SCD sensor (L=120 μm) as a function of actuated voltage at (a) room temperature and (b) 500℃. (c) Dependence of amplitude peak of resonance spectrum of the WC/Ti/SCD sensor on the actuation voltage at room temperature and 500℃. (d) Resonance spectra shifts of the WC/Ti/SCD sensor as a function of the measurement temperature. (e) Dependence of the resonance frequency shift of the WC/Ti/SCD sensor on the temperature. (f) Variation of Q factor of the WC/Ti/SCD sensor with the temperature increasing.�Fig. 4. Resonance spectra of the FeGa/Ti/SCD sensor (L=160 μm) vs the actuation voltage at (a) room temperature and (b) 500℃. (c) Dependence of amplitude peak of resonance spectrum of the FeGa/Ti/SCD sensor on the actuation voltage at room temperature and 500℃. (d) Resonance spectra shifts of the FeGa/Ti/SCD sensor induced by applying the magnetic field as a function of the measurement temperature. (e) Resonance frequency shift of the FeGa/Ti/SCD sensor vs the magnetic field at different evaluated temperature. (f) Q variations of the FeGa/Ti/SCD sensor with the measurement temperature without and with applying magnetic field.