Michihiko Nishigaki

RF-MEMS Tunable Capacitor With 3 V Operation Using Folded Beam Piezoelectric Bimorph Actuator

Tunable capacitors with high tuning range and high Q-factors are indispensable for realizing reconfigurable radio-frequency (RF) circuits for multiband/multimode next-generation mobile wireless communication terminals. A novel RF microelectromechanical systems tunable capacitor having a piezoelectric bimorph actuator has been developed using a complementary metal-oxide-semiconductor compatible surface micromachining process. Folded beam piezoelectric actuators were introduced to cancel curling of the actuator beam due to residual stress. The continuous wide tuning ratio of three was realized at an operation voltage of less than 3 V for the first time

Piezoelectric RF MEMS tunable capacitor with 3V operation using CMOS compatible materials and process

A RF MEMS tunable capacitor having a piezoelectric bimorph actuator was developed using a CMOS compatible surface micromachining process. Folded beam piezoelectric actuators were introduced to cancel carling. Its continuous wide tuning ratio of 3 was realized at less than 3 V operations for the first time

Piezoelectric MEMS Variable Capacitor for a UHF Band Tunable Built-in Antenna

A UHF band tunable built-in antenna is realized using piezoelectric MEMS variable capacitors. The variable capacitor, which is driven by a piezoelectric actuator, has a tuning ratio of 11 with control voltage ranging from 0 to 8 V and quality factor of more than 37 at 650 MHz. The built-in antenna, which is an inverted-F antenna, is mounted at the top of an upper PCB board of a clamshell mobile phone, and the antenna element has a meander shape for a built-in structure. In the tunable built-in antenna, the variable capacitor is connected to one point of the meander structure of the built-in antenna. The antenna covers a frequency from 510 to 800 MHz with an efficiency of more than -3.5 dB, or the relative bandwidth of 44% by changing the value of the variable capacitor.

Optimization of Deposition Process and Microscopic Characterization of Highly Oriented Aluminum Nitride Thin Films for Bimorph Structures of Piezoelectric Tunable Capacitors

Film deposition with RF sputtering to control residual stress in aluminum nitride (AlN) thin films has been investigated to fabricate the bimorph actuator for a piezoelectric tunable capacitor with low-voltage operation. The effects of conditions in sputtering and surface cleaning were studied both to obtain a preferable film orientation for piezoelectric actuation and to suppress structural deformation of the cantilever due to the residual stress in films. Microscopic analysis revealed that (0001)-oriented AlN and (111)-oriented Al films were epitaxially grown at each interface in the bimorph structure. The current–voltage (I–V) measurements showed a leakage current of less than 5 ×10-5 A m-2 in 500-nm thick AlN films up to 30 V. The effect of optimization of process parameters was demonstrated by the capacitance–voltage (C–V) characteristics of the folded-beam tunable capacitor, in which the suppression of residual stress in piezoelectric layers was shown to be effective to obtain low-voltage operation.

Fabrication and Performance of Piezoelectric MEMS Tunable Capacitors Constructed with AlN Bimorph Structure

Fabrication process and electrical performances in a novel piezoelectric tunable capacitor have been studied. The piezoelectric bimorph structure of AlN/Al multilayer was fabricated with CMOS compatible process. The voltage dependence of actuation showed a good agreement with those of theoretical calculation, whereas stress measurements showed that suppression of residual stress in AlN layers was most critical for curling in the beams. Suppression of the distance between capacitor electrodes realized by the folded-beam type design resulted in capacitance tuning ratio of over ten at 3V. High frequency measurements up to 20GHz revealed that the tunable capacitor maintained a capacitive property up to 18GHz

A 6Gbps 3mW optical receiver with DCOC-combined ATC in 65nm CMOS

This paper presents a 0.48-mW/Gbps optical receiver in a 65-nm CMOS process. The receiver includes a tran-simpedance amplifier (TIA) with a DC offset canceler (DCOC) combined with an autothreshold controller (ATC) function for providing low-power, area-efficient single-ended-to-differential conversion. The fabricated 6-Gbps optical receiver consumes 2.86-mW power and achieves less than −3.8-dBm sensitivity at a BER of 10−11.

Stable multi-step capacitance control with binary voltage operation at +/-3V in integrated piezoelectric RF MEMS tunable capacitors

The design and operation technique for a stable capacitance control in piezoelectric RF MEMS tunable capacitors have been investigated. Four folded-beam capacitors composed of piezoelectric aluminum nitride thin films were integrated in the quadruple capacitor and each folded-beam capacitor showed uniform operation voltage of less than 3V. A stable multi-step capacitance control was realized with the binary voltage operation at +/-3V, where each capacitor could be handled at binary state of capacitance due to its saturation characteristics. Eight levels of capacitance value up to 1.5pF with a step of 0.13pF to 0.16pF were realized.

Ultracompact 4×3.4 Gbps optoelectronic package for an active optical HDMI cable

Refering to the increasing demand for extended transmission distances of high-definition video in consumer electronics we present a composite optoelectronic high-definition multimedia interface (HDMI) cable that replaces the four electrical transition-minimized differential signal video channels by a 4×3.4 Gb/s optical fiber link, the currently maximum specified bit rate. This improves the signal quality after 10 m transmission compared to a passive electrical cable significantly and enables even longer cable lengths or higher transmission rates. At the same time we developed a compact package of both the optical sub-assembly and its adjoining control ICs that fits inside the cable connector. We outline the package assembly and present basic transmission characteristics, as well as confirm 1080p video transmission over 10 m.

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We introduce an extremely thin 50/125 perfluorinated graded-index plastic optical fiber (POF) and its application in a 4×10 Gb/s optical link including our optical sub-assembly (OSA). We outline the main characteristics of the POF before the introduction of the fibers to our already established OSA is explained. Particularly low attenuation with error-free transmission down to a bending radius of 1 mm is presented in comparison to a quartz optical fiber. Furthermore eye diagrams of all four channels after 5 m over POF at 10 Gb/s are presented. Bit error rate for all channels is less than 10-12 and remains constant when another channel is being driven simultaneously.

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A novel RF MEMS tunable capacitor having W-shaped folded beam piezoelectric bimorph actuator using a CMOS compatible surface micromachining process has been proposed. The structure almost completely compensates the curling of the beams due to unbalanced residual stress and thermal expansion mismatch, and assures high reproducibility and negligible temperature dependence. Cyclic and static lifetime tests at as high as 9V had slight effects on the C-V characteristics. The high reproducibility and reliability assure the capacitors are promising as key components in reconfigurable RF systems, such as tunable antennas, tunable filters and tunable impedance networks.