We report on the first experimental demonstration of five self-sustaining feedback oscillators referenced to a single multimode resonator, using piezoelectric aluminum nitride on silicon (AlN/Si) ...microelectromechanical systems (MEMS) technology. Integrated piezoelectric transduction enables efficient readout of five resonance modes of the same AlN/Si MEMS resonator, at 10, 30, 65, 95, and 233 MHz with quality (<inline-formula> <tex-math notation="LaTeX">{Q} </tex-math></inline-formula>) factors of 18 600, 4350, 4230, 2630, and 2138, respectively, at room temperature. Five stable self-sustaining oscillators are built, each referenced to one of these high-<inline-formula> <tex-math notation="LaTeX">{Q} </tex-math></inline-formula> modes, and their mode-dependent phase noise and frequency stability (Allan deviation) are measured and analyzed. The 10, 30, 65, 95, and 233 MHz oscillators exhibit low phase noise of −116, −100, −105, −106, and −92 dBc/Hz at 1 kHz offset frequency, respectively. The 65 MHz oscillator yields the Allan deviation of <inline-formula> <tex-math notation="LaTeX">4\times 10^{-{9}} </tex-math></inline-formula> and <inline-formula> <tex-math notation="LaTeX">2\times 10^{-{7}} </tex-math></inline-formula> at 1 and 1000 s averaging time, respectively. The 10 MHz oscillator's low phase noise holds strong promise for clock and timing applications. The five oscillators' overall promising performance suggests suitability for multimode resonant sensing and real-time frequency tracking. This work also elucidates mode dependency in oscillator noise and stability, one of the key attributes of mode-engineerable resonators.
Cubic silicon carbide is a promising material for Micro Electro Mechanical Systems (MEMS) applications in harsh environ-ments and bioapplications thanks to its large band gap, chemical inertness, ...excellent corrosion tolerance and capability of growth on a Si substrate. This paper reports the piezoresistive effect of p-type single crystalline 3C-SiC characterized at high temperatures, using an in situ measurement method. The experimental results show that the highly doped p-type 3C-SiC possesses a relatively stable gauge factor of approximately 25 to 28 at temperatures varying from 300 K to 573 K. The in situ method proposed in this study also demonstrated that, the combination of the piezoresistive and thermoresistive effects can increase the gauge factor of p-type 3C-SiC to approximately 20% at 573 K. The increase in gauge factor based on the combination of these phenomena could enhance the sensitivity of SiC based MEMS mechanical sensors.
This paper reports on the investigation of anomalous low quality factors (<inline-formula> <tex-math notation="LaTeX">{Q}\text{s} </tex-math></inline-formula>) in AlN thin film-based length ...extensional (LE)-mode resonators using finite element method (FEM), analytical modeling, and experimental techniques. Different heterostructures of LE resonators having Al/AlN/Si, Al/AlN, AlN/Si, and Si are designed and fabricated using standard MEMS processes. Experimental <inline-formula> <tex-math notation="LaTeX">{Q}\text{s} </tex-math></inline-formula> along with resonances are obtained using electrical and optical readout and are compared with the modeled and analytically obtained <inline-formula> <tex-math notation="LaTeX">{Q}\text{s} </tex-math></inline-formula>. The results show that the thermoelastic damping (TED) in metal electrode, anchor loss, and charge redistribution loss are not the dominant loss mechanisms. With the help of Mason's network modeling, we investigated the dielectric loss, which is also observed to be negligible for these resonators. An internal mechanical loss, originating from the columnar growth of AlN and observed using Mason's model, is proved to be the dominant loss mechanism. This observation is confirmed and reinforced by the COMOSL's FEM analysis of TED in AlN, having columnar growth effect and by experimental results. 2018-0258
Tuning the natural frequency of a resonator is an innovative approach for the implementation of mechanical resonators in a broad range of fields such as timing applications, filters or sensors. The ...conventional electrothermal technique is not favorable towards large tuning range because of its reliance on metallic heating elements. The use of metallic heaters could limit the tuning capability due to the mismatch in thermal expansion coefficients of materials forming the resonator. To solve this drawback, herein, the design, fabrication, and testing of a highly-doped SiC bridge resonator that excludes the use of metallic material as a heating element has been proposed. Instead, free-standing SiC structure functions as the mechanical resonant component as well as the heating element. Through the use of the Joule heating effect, a frequency tuning capability of almost ∆f/fo ≈ 80% has been demonstrated. The proposed device also exhibited a wide operating frequency range from 72.3 kHz to 14.5 kHz. Our SiC device enables the development of highly sensitive resonant-based sensors, especially in harsh environments.
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•Free-standing silicon carbide (SiC) bridges function as both resonant structure and heating element.•Ultra-large frequency tuning capability of almost 80% was demonstrated for SiC resonators by thermal stress.•Frequency tunability of SiC micromechanical resonators is dependent on stress induced by Joule heating.
The current mechanism and effects of external transverse stress in the 110 orientation on the electrical properties of a single crystal (100) p-3C-SiC/p-Si heterojunction diode are reported for the ...first time. It has been observed that the current flow in the heterojunction is due to tunneling through the triangular potential barrier formed due to valence band offset between Si and SiC. The applied stress produces small changes in tunneling current when stress is increased from 0 to 308 MPa. The observed increase in current at 0.24 V is 10% at maximum stress of 308 MPa. The increase of tunneling current when applying stress is explained in terms of stress, which alters the out-of-plane effective mass, and the effective tunneling barrier height of holes in top subbands of p-type Si.
Semiconductor nanowires are widely considered as the building blocks that revolutionized many areas of nanosciences and nanotechnologies. The unique features in nanowires, including high electron ...transport, excellent mechanical robustness, large surface area, and capability to engineer their intrinsic properties, enable new classes of nanoelectromechanical systems (NEMS). Wide bandgap (WBG) semiconductors in the form of nanowires are a hot spot of research owing to the tremendous possibilities in NEMS, particularly for environmental monitoring and energy harvesting. This article presents a comprehensive overview of the recent progress on the growth, properties and applications of silicon carbide (SiC), group III‐nitrides, and diamond nanowires as the materials of choice for NEMS. It begins with a snapshot on material developments and fabrication technologies, covering both bottom‐up and top‐down approaches. A discussion on the mechanical, electrical, optical, and thermal properties is provided detailing the fundamental physics of WBG nanowires along with their potential for NEMS. A series of sensing and electronic devices particularly for environmental monitoring is reviewed, which further extend the capability in industrial applications. The article concludes with the merits and shortcomings of environmental monitoring applications based on these classes of nanowires, providing a roadmap for future development in this fast‐emerging research field.
Wide bandgap semiconductor nanowires with unique properties and advanced fabrication/integration technologies set a new class of nanosensing and electronic applications. Implementation of these smart devices such as gas sensors, photodetectors, wearable devices, strain sensors, and energy harvesters into environmental monitoring systems offers promising solutions for critical environmental challenges.
In article number 2004655, Tuan‐Anh Pham, John A. Rogers, Nam‐Trung Nguyen, Hoang‐Phuong Phan, and co‐workers demonstrate a transfer printing technique to form multiple silicon carbide ...microarchitectures onto polymers. This approach uses a dissolvable metal nanomembrane as a sacrificial layer, establishing the nano‐materials basis and methodology for the fabrication of flexible bio‐barriers and electronics, as a critical step towards long‐lived implanting applications.
Silicon carbide (SiC) has been extensively investigated in the last decade, specifically for applications in harsh environments. However, most SiC sensors require an external power supply, which ...cannot operate at high temperatures. This letter develops a new sensing technology in a SiC platform based on near field communication to eliminate the requirement for wired power sources. The 3C-SiC temperature sensors were fabricated from a SiC-on-insulator substrate formed by anodic bonding. The sensors functioned based on the thermoresistance of the SiC films with the high TCR of -13 000 ppm/K at 300 K and -3 000 ppm/K at 600 K. The resistance change of the sensors was wirelessly measured using a reading coil placed outside of the heating chamber, showing a significant resonant-frequency-shift (-400 ppm/K at 600 K) of the coupling impedance under temperature variation. The proposed technique is promising for the development of wireless wide-band-gap sensors used in extreme conditions.
In this work, we demonstrate highly thermosensitive silicon nanowires (SiNWs) for thermal-sensing applications. Crystalline Si was amorphized by Focused Ion Beam in the fabrication process of the ...SiNWs, and subsequently recrystallized by a thermal annealing process to improve their electrical conductivity. A temperature coefficient of resistance (TCR) from −8000ppm/K to −12,000ppm/K was measured for the SiNWs. This large negative TCR is attributed to the boundary potential barrier of 110meV between silicon crystallites in the poly crystalline SiNWs.
•Silicon films were amorphized by FIB and recrystallized using thermal annealing.•A large negative temperature coefficient of resistance of SiNWs was achieved.•The thermosensitivity is explained using boundary theories for polycrystalline Si.
We report for the first time the thermoresistive property of p-type single crystalline 3C–SiC (p-3C–SiC), which was epitaxially grown on a silicon (Si) wafer, and then transferred to a glass ...substrate using a Focused Ion Beam (FIB) technique. A negative and relatively large temperature coefficient of resistance (TCR) up to −5500 ppm K −1 was observed. This TCR is attributed to two activation energy thresholds of 45 meV and 52 meV, corresponding to temperatures below and above 450 K, respectively, and a small reduction of hole mobility with increasing temperature. The large TCR indicates the suitability of p-3C–SiC for thermal-based sensors working in high-temperature environments.
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