K. N. Bhadri Narayanan

Bio: K. N. Bhadri Narayanan is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Resonator & Q factor. The author has an hindex of 1, co-authored 2 publications receiving 3 citations.

Design and fabrication of 1 GHz lateral TPoS MEMS resonator for RF front end applications

Abstract: This paper reports on design, fabrication and characterization of laterally excited thin film piezoelectric on Silicon (TPoS) MEMS resonators of resonance frequency around 1 GHz. Devices were fabricated on 5 μm SOI and 0.5 μm Aluminium Nitride piezoelectric film. We studied the effect of the number of anchors attached to the resonator and the width of the resonator on Q-factor and motional resistance. Measured characteristics of the device with Phononic crystal (PnC) tether showed a resonance peak at 969.22 MHz with motional resistance 2.9 kΩ and Q-factor of 1998. The motional resistance could be reduced to 770 Ω for wider devices.

Design, Modeling and Fabrication of TPoS MEMS Resonators With Improved Performance at 1 GHz

Abstract: In this work, the effects of physical dimensions such as length, width and thickness as well as the mode of vibration and the number of anchors on the performance of longitudinal thin film piezoelectric on silicon (TPoS) MEMS resonators have been studied. TPoS resonators, designed for a resonant frequency of around 1 GHz, were fabricated with a 4 mask CMOS compatible process. A $225~\mu \text{m}$ wide resonator excited in its $23^{rd}$ order had an unloaded quality factor of 9453 (in vacuum), which is the highest value reported so far for similar resonators, motional resistance of $107~\Omega $ and linear thermal coefficient of frequency of -28.4 ppm. We have also studied and modeled the different loss mechanisms in these devices. The model matches well with measured results for resonators of different geometries, modes of vibrations and number of anchors. [2020-0397]

Optimization of Anchor Placement in TPoS MEMS Resonators: Modeling and Experimental Validation

Abstract: In this paper, a semi-analytical model is derived to calculate the anchor loss of TPoS resonators operating in higher-order length extensional modes. This model provides valuable insights on the effect of order, device dimensions, position and number of anchors on the quality factor (Q) of these resonators. Results from this model are in close agreement with the FEM simulations. The optimum position, dimension, and the number of anchors to deliver the highest Q are also discussed. Predictions of the model are validated through characterization of TPoS resonators fabricated to operate at a resonant frequency of around 1 GHz with different number of anchor pairs and position. A $23^{rd}$ order resonator with a W/L ratio of 1.5 with three pairs of anchors placed at positions suggested by the model gave a loaded Q of 4431, which is 65% more than the conventional case where anchors are uniformly placed towards the edge, and also an improvement in the insertion loss by 5.5 dB compared to the latter. For resonators where the anchor loss is predominant, our results show that the performance can be improved by placing the anchors at the optimum position, closer to the middle of the resonator than the conventional scheme where anchors are uniformly placed towards the edge.

A Thin-Film Piezoelectric-on-Silicon MEMS Oscillator for Mass Sensing Applications

Abstract: In this study, a Thin-film Piezoelectric-on-Silicon (TPoS) MEMS oscillator is successfully demonstrated that uses lead zirconate titanate (PZT) thin-film piezoelectric layer deposited on a single-crystal silicon substrate to realize a length-extensional mode resonator, having a resonant frequency of 5.12 MHz and a quality factor ( ${Q}$ ) of 311. For closed-loop implementation, a commercial Lock-in amplifier with a Phase Locked Loop (PLL) facility was used to fulfill the Barkhausen criteria for oscillation. The mass resolution and sensitivity of the proposed mass sensor are 0.54 pg and 4.96 Hz/pg, respectively. Finally, a board-level sustaining circuit, which includes a transimpedance amplifier (TIA) and an attenuator is integrated with the TPoS MEMS resonator for oscillation to achieve a portable sensor. Phase noise of −104.11 dBc/Hz at 1 kHz offset was recorded under ambient pressure and room temperature for a carrier frequency of 5.12 MHz. The mass resolution for the board-level mass sensor implemented in this work is 0.15 pg.

Design, Modeling and Fabrication of TPoS MEMS Resonators With Improved Performance at 1 GHz

Abstract: In this work, the effects of physical dimensions such as length, width and thickness as well as the mode of vibration and the number of anchors on the performance of longitudinal thin film piezoelectric on silicon (TPoS) MEMS resonators have been studied. TPoS resonators, designed for a resonant frequency of around 1 GHz, were fabricated with a 4 mask CMOS compatible process. A $225~\mu \text{m}$ wide resonator excited in its $23^{rd}$ order had an unloaded quality factor of 9453 (in vacuum), which is the highest value reported so far for similar resonators, motional resistance of $107~\Omega $ and linear thermal coefficient of frequency of -28.4 ppm. We have also studied and modeled the different loss mechanisms in these devices. The model matches well with measured results for resonators of different geometries, modes of vibrations and number of anchors. [2020-0397]

Extraction of D 31 Piezoelectric Coefficient of AlN Thin Film

Abstract: Piezoelectric materials have the property of electromechanical coupling, which is very useful in Micro Electro Mechanical Systems (MEMS). Aluminium Nitride (AlN) thin film is an ideal candidate for resonators in on-chip front end circuit. The piezoelectric coupling coefficient d 31 is responsible for the excitation in longitudinal mode resonators. Direct measurement of the value of d31 is still an area of research. We propose a method to extract the piezoelectric coefficient d31 from the transmission characteristics of a resonator. The average extracted value of d31 is -0.943 pC/N with standard deviation 0.21 pC/N, which is comparable with reported values.

Effect of Phononic Crystal Orientation on AlN-on-Silicon Lamb Wave Micromechanical Resonators

Abstract: Phononic crystals (PnCs) have been used to boost the quality factor (Q) of AlN-on-Silicon Lamb Wave Resonators (LWRs). But most reports on applying PnCs to resonators have focused on the common $< 110>$ orientation within (100) silicon. Little is known on the applicability of other crystal orientations. In this work, we explore the effect of orientation on the acoustic band gap (ABG) of two PnC designs and their effect on boosting Q: a disk PnC and a ring PnC. From Finite Element simulation, we show that the disk PnC’s ABG is insensitive to orientation while adding a hole into the disk to form a ring changes its ABG to be much more sensitive to orientation. Leveraging the PnCs as anchoring boundary of LWRs, the disk PnC exhibits comparable effectiveness to boost Q >11,000 in the $< 110>$ and $< 100>$ directions while the ring PnC is effective only in the $< 110>$ direction. We further corroborate these trends by incorporating the disk PnC into delay lines in either crystal axis.

Effect of Phononic Crystal Orientation on AlN-on-Silicon Lamb Wave Micromechanical Resonators

Abstract: Phononic crystals (PnCs) have been used to boost the quality factor (Q) of AlN-on-Silicon Lamb Wave Resonators (LWRs). But most reports on applying PnCs to resonators have focused on the common $< 110>$ orientation within (100) silicon. Little is known on the applicability of other crystal orientations. In this work, we explore the effect of orientation on the acoustic band gap (ABG) of two PnC designs and their effect on boosting Q: a disk PnC and a ring PnC. From Finite Element simulation, we show that the disk PnC’s ABG is insensitive to orientation while adding a hole into the disk to form a ring changes its ABG to be much more sensitive to orientation. Leveraging the PnCs as anchoring boundary of LWRs, the disk PnC exhibits comparable effectiveness to boost Q >11,000 in the $< 110>$ and $< 100>$ directions while the ring PnC is effective only in the $< 110>$ direction. We further corroborate these trends by incorporating the disk PnC into delay lines in either crystal axis.