Research/Monolithic Integration of Microwave Passive Devices with RF-MEMS

2019-02-17 (日) 23:24:47 (542d)

機能レイヤ分離設計によるSOI RF−MEMS受動素子に関する研究
A Study on SOI RF-MEMS Passive Devices by Functional Layer-wise Design Method


A novel design of switched-line RF-MEMS (radio frequency micro electro mechanical systems) phase-shifter for the X-Ku band (8 ~ 18 GHz) has been successfully developed by monolithically integrating electrostatic MEMS actuators with movable coplanar waveguides made of single crystalline silicon. MEMS and RF waveguides designs have been performed with minimum geometrical conflicts thanks to the layer-wise functional allocation method, where double surfaces of SOI (silicon on insulator) wafer are used.


We have successfully demonstrated the design principle on a 1-bit phase-shifter of 22.5 degrees at 12 ~ 13 GHz and obtained insertion loss of 1.6 ~ 1.9 dB/bit, return loss of -9 ~ -13 dB, and isolation of -40 dB by the electrostatic operation under 40 V.




APAA (Active Phase Array Antenna) is an agile antenna that can electronically control the direction of radiation at fast speed. Due to the large number of arrayed electronic components such as solid-state amplifiers and phase shifters, however, the cost of constructing an APAA is not in a range that a commercial application can afford. In this work, we aim to lower the cost of such system by newly using the MEMS technology to construct a monolithic phase shifter (4-bit).


本研究で試作した移相器は、長短2本の遅延線のうち、一方をスイッチによって選択する線路選択型の移相器です。この位相器を構成するには、1入力2出力(Single Pole Double Throw, SPDT)スイッチが2系統必要です(Dual SPDS)。

A switch is used to choose one of the longer or shorter delay lines to control the phase delay. One bit of such phase shifter needs two pieces of SPDT (Single Pole Double Throw) switches or Dual-SPDT.

RF-MEMS Structure by Layer-separation Design



We adopted our own MEMS design technique called "Layer Separation" to construct an RF-MEMS switch; the handle substrate of an SOI layer is used as a body of CPW (co-planar waveguide) cantilever beam that laterally swings to close a metal-to-metal contact, while the SOI active layer is used to integrate an electrostatic micro actuator. The developed switch structures have a compatibility and scalability to an N-bit monolithic switch integrated in a silicon substrate of high impedance.

Bulk Micromachining



In this work, we used a thick plated gold (4 microns) on the handle wafer side of an SOI, and used it as a CPW contact as well as an etching mask for the DRIE processe.


As a proof-of-concept level demonstration, we have developed a unit cell of 1-bit monolithick RF-MEMS switch and confirmed its electrostatic operation and high frequency performances.

Openhouse Poster

We have developed a monolithically integrated RF-MEMS phase-shifter for a 12 GHz application by improving the previously reported dual SPDT RF-MEMS switch. SOI substrate was used to accommodate the electrostatic actuation mechanism in the 30 mm-thick silicon layer and to allocate mechanically movable waveguides on the 100 mm-thick substrate; electroplating of 4 mm thick gold was applied onto the waveguide surface to lower the microwave insertion loss.

At the same time, high resistance silicon was used for the handle wafer of the SOI to minimize dielectric loss. Electrostatic operation at 40 V was successfully demonstrated to present a 1-bit phase shifter of 22.5 degrees at 12 ~ 13 GHz, insertion loss of 1.6 ~ 1.9 dB/bit, return loss of -9 ~-13 dB, and isolation of less than -40 dB.