Gwendolyn Hummel

Aluminum Nitride Cross-Sectional Lamé Mode Resonators

This paper demonstrates a new class of AlN-based piezoelectric resonators for operation in the microwave frequency range. These novel devices are identified as cross-sectional-Lamé-mode resonators (CLMRs) as they rely on the piezoelectric transduction of a Lamé mode, in the cross section of an AlN plate. Such a 2-D mechanical mode of vibration, characterized by motion along both the lateral and the thickness directions, is actuated and sensed piezoelectrically through the coherent combination of the e31 and e33 piezoelectric coefficients of AlN. This special feature enables the implementation of CLMRs with high values of electromechanical coupling coefficient. In particular, we experimentally demonstrated kt2 values in excess of 4.6% and 2.5% in CLMRs using, respectively, two or one metallic interdigitated metallic electrodes, and operating around 1 and 2.8 GHz. Furthermore, despite the dependence of the cross-sectional Lamé mode on both the thickness and the width of the AlN plate, lithographic tunability of the resonance frequency, by changing only the in-plane dimensions of the device, can be achieved without a substantial degradation of kt2. The capability of achieving high kt2 and multiple operating frequencies on the same chip, without additional fabrication costs (lithographic tunability of the resonance frequency), makes this technology one of the best candidates for the implementation of multifrequency and low insertion loss filter banks for reconfigurable radiofrequency front ends.

Cross-Sectional Lamé Mode Ladder Filters for UHF Wideband Applications

This letter reports on the first demonstration of ladder filters based on the recently demonstrated cross-sectional Lamé mode resonator (CLMR) technology. These filter prototypes show a fractional bandwidth (BW3dB) as high as 3.3% and an insertion loss as low as 0.4 dB. As the resonance frequency of CLMRs can be lithographically controlled without significantly degrading their electromechanical coupling coefficient (k2t), multiple contiguous frequency bands can be covered by this filter technology without adding fabrication complexity. This unique feature addresses one of the most crucial challenges associated with the development of miniaturized mobile platforms adopting carrier-aggregation. Furthermore, the capability of achieving large BW3dB, around lithographically defined center frequencies, enables the fabrication of transmit and receive modules of the next-generation radio-frequency front ends on the same chip without adding fabrication steps.

Phase change material programmable vias for switching and reconfiguration of Aluminum Nitride piezoelectric MEMS resonators

This paper reports on the first demonstration of an innovative approach to switching and reconfiguration of Aluminum Nitride (AlN) piezoelectric Micro Electro Mechanical System (MEMS) resonators using phase change material (PCM) programmable vias. A reconfigurable resonator prototype was fabricated by integrating 2 Ge₅₀Te₅₀ vias in the design of a 200 MHz contour-extensional mode resonator. The capability to reconfigure the device to operate in 3 different states, maintaining constant electromechanical performance (resonator figure of merit, FOM=k_t²·Q≈7) was demonstrated: (1) High Impedance state (resonator static capacitance, C₀≈660 fF, motional resistance, R_m≈225 Ω), (2) Low Impedance state (C₀≈1409 fF; R_m≈90 Ω), and (3) Short state (the resonator is reconfigured into a short circuit).

Reconfigurable mode of vibration in AlN MEMS resonators using phase change materials

This paper presents the first demonstration of a new approach to dynamic reconfiguration of the mode of vibration in AlN piezoelectric MEMS resonators using phase change material (PCM) based switchable electrodes. This innovative design solution enables effective ON/OFF switching of the acoustic resonance (~4.75X impedance variation at resonance), and reconfiguration of the device electromechanical coupling (kt12: 0 - 0.553%), capacitance (C: 309 - 937 fF), and operating frequency (f1~257 MHz, f2~378 MHz). Such unique reconfiguration capabilities can potentially lead to the implementation of filter architectures (exclusively based on AlN/PCM high performance resonators and capacitors) whose frequency, order, bandwidth, and roll-off can be dynamically reconfigured.

RF Passive Components Based on Aluminum Nitride Cross-Sectional Lamé-Mode MEMS Resonators

This paper presents a new class of monolithic integrated RF passive components based on the recently developed aluminum nitride (AlN) MEMS cross-sectional Lamé-mode resonator (CLMR) technology. First, we experimentally demonstrate a 920-MHz CLMR showing the values of electromechanical coupling coefficient (k_t²) and quality factor (Q_load) in excess of 6.2% and 1750, respectively. To the best our knowledge, the resulting figure of merit (= Q·k_t²), in excess of 108, is the highest ever reported for AlN-based piezoelectric resonators using interdigitated metallic electrodes (IDTs) and operating in the same frequency range. Second, we report the measured performance of an 870-MHz ladder filter, synthesized using three degenerate CLMRs. This device shows the values of fractional bandwidth (BW_3dB) in excess of 3.8% and an insertion loss of ~1.5 dB. Finally, we report the performance of the first piezoelectric transformer (PT) based on the CLMR technology. This device, dubbed “cross-sectional Lamé-mode transformer,” exploits the high-k_t² of the CLMR technology to achieve high values of open-circuit voltage-gains (G_v) in excess of 39. To the best of our knowledge, such a high G_v-value is the highest ever reported for MEMS-based PTs operating in the microwave frequency range.

1.02 GHz cross-sectional Lamé mode resonator with high KT2 exceeding 4.6%

This paper demonstrates a new class of AlN-based piezoelectric resonators for operation in the microwave frequency range. These novel devices are identified as Cross-Sectional-Lamé-Mode resonators (CLMRs) as they rely on the piezoelectric transduction of a Lamé mode, in the cross-section of an AlN plate. Such 2-dimensional (2D) mechanical mode of vibration, characterized by motion along both the lateral and the thickness directions, is actuated and sensed piezoelectrically through the coherent combination of the en and en piezoelectric coefficients of AlN. This special feature enables the implementation of CLMRs with high values of electromechanical coupling coefficient (kt2). We demonstrate a kt2 value in excess of 4.6% in a CLMR operating around 1.02 GHz. Such kt2 value is the highest ever reported among AlN resonators employing interdigital-metal-electrodes (IDTs) to actuate and to sense the mechanical motion.

Switchable 2-port Aluminum Nitride MEMS resonator using monolithically integrated 3.6 THz cut-off frequency phase-change switches

This work presents the first experimental demonstration of an intrinsically switchable Aluminum Nitride (AlN) 2-port MEMS resonator using 3 monolithically integrated chalcogenide phase change material (PCM) switches.

Highly reconfigurable Aluminum Nitride MEMS resonator using 12 monolithically integrated phase change material switches

This paper presents the first demonstration of a frequency reconfigurable and programmable Aluminum Nitride (AlN) piezoelectric MEMS resonator using phase change material (PCM) based switchable electrodes. For the first time, 12 miniaturized (2 μm×2 μm) PCM switches are monolithically integrated with an AlN MEMS resonator and used to reconfigure the terminal connections of the individual metal fingers composing the device interdigital transducer (IDT). This innovative design solution provides high ON/OFF ratio switching of the acoustic resonance (~28X impedance variation at resonance), and reconfiguration of the device electromechanical coupling (kt2: 0-1.32%), capacitance (C: 125-1,134 fF), and operating frequency (f1~181.3 MHz, f2~385.4 MHz).

Reconfigurable Piezoelectric MEMS Resonator Using Phase Change Material Programmable Vias

This paper reports on the demonstration of a reconfigurable aluminum nitride (AlN) piezoelectric microelectromechanical systems (MEMS) resonator using phase change material (PCM) programmable vias. Two 10-μm × 10-μm Ge₅₀Te₅₀ PCM programmable vias are monolithically integrated with a piezoelectric MEMS resonator, and used to dynamically reconfigure the terminal connections of its top and bottom electrodes, which determine the distribution of the electric field across the piezoelectric layer and therefore the equivalent electrical impedance of the resonator. The ability to reconfigure the device to operate in four different states is experimentally demonstrated: 1) lateral field excitation mode (both vias OFF); 2) resonator static capacitance, C₀ ≈ 484 fF; 3) motional resistance, R_m ≈ 320 Ω; 4) thickness field excitation mode-high impedance (via 1 ON, C₀ ≈ 564 fF; R_m ≈ 470 Q); 5) thickness field excitation mode-low impedance (via 2 ON, C₀ ≈1459 fF; R_m ≈155 Q); and 6) SHORT (both vias ON, the resonator is reconfigured into a short circuit). This paper sets a milestone toward the demonstration of an innovative technology platform, based on the monolithic integration of AlN resonators and PCM switches, capable of delivering highly reconfigurable radio frequency components, enabling new radio architectures with enhanced spectrum coverage.

Aluminum Nitride cross-sectional Lamé mode resonators with 260 MHz lithographic tuning capability and high kt 2 > 4%

We experimentally demonstrate Aluminum Nitride (AlN) cross-sectional Lamé mode resonators (CLMRs) operating in the microwave frequency range and showing high Qkt2 products (FoM) in excess of 85. Such feature enables low motional resistance (Rm) values (37 Ω) in CLMRs characterized by low static capacitance (Co) approaching 66 fF. In addition, the ability of CLMRs to simultaneously achieve high kt2 (> 4%) and a lithographic frequency tunability (> 260 MHz around 900 MHz) is experimentally demonstrated, for the first time, in this work. Such important feature renders CLMRs promising candidates to replace off-chip Surface Acoustic Wave (SAW) devices in lithographically defined filters for next-generation wireless communication platforms.