Chang-Han Je

Fabrication of morphological defect-free vertical electrodes using a (1 1 0) silicon-on-patterned-insulator process for micromachined capacitive inclinometers

This paper presents a novel fabrication method of scalloping-free and footing-free vertical electrodes for micromachined capacitive inclinometers with a high sensing resolution. The proposed fabrication method is based on additional crystalline wet etching of a (1 1 0) silicon that is bonded to a silicon substrate with a patterned insulator layer. The sensing electrodes, which are aligned to the (1 1 1) plane, have very smooth sidewalls because the morphological defects formed by the silicon deep reactive ion etching (DRIE) process are drastically reduced in the crystalline wet etching. The fabricated capacitive inclinometer with smooth sensing electrodes was evaluated in terms of capacitance change and resolution. The capacitance of the fabricated inclinometer is changed from −0.246 to 0.258 pF for the inclination angle (−90° to 90°). The temporal deviation of the capacitance is as small as 0.2 fF, which leads to a high resolution of 0.1° or less for ±45°.

A surface-micromachined MEMS acoustic sensor with X-shape bottom electrode anchor

A surface-micromachined capacitive-type micro-electro-mechanical system (MEMS) acoustic sensor with X-shape bottom electrode anchor on a Si substrate is presented. As it is designed to be implemented on only one side of a substrate for a simple monolithic integrated process, this sensor has X-shape bottom electrode anchor fabricated. The anchor operates to remove the back side process of wafer for a conventional back chamber because the chamber is formed through Si surface etching by an isotropic dry etcher of XeF2. The Si MEMS acoustic sensor proposed in this paper has a diameter of 300 µm and a back chamber depth of 25 µm. It shows a pull down voltage of 9.1 V at 1 kHz and a zero-bias capacitance of 1.87 pF. Additionally, the sensor has an open-circuit sensitivity of 0.57 mV/Pa at 1 kHz on a bias of 5 V.

A surface-micromachined MEMS acoustic sensor with back-plate anchors of 100 µm depth

A surface-micromachined capacitive-type microelectro-mechanical system (MEMS) acoustic sensor with back-plate anchors of 100 µm depth is presented. The sensor is implemented by a simple front-side fabrication process of a Si substrate with a compatibility with a full CMOS process. For only the front-side process, the back-plate anchors are placed under a back-plate and inserted very deeply into the substrate by Deep Reactive-Ion Etching (DRIE), and their upper part is covered with a thick back-plate of 2.9 µm. Also, a diaphragm is composed entirely of standard CMOS process layers for a monolithic integration. It has a diameter of 500 µm and a back chamber depth of around 80 µm. After a sacrificial layer of 2.2 µm is released, the back chamber is realized by XeF2 etcher as well as the back-plate anchors, simultaneously. Thus, it shows a measured zero-bias capacitance (Cmea) of 1.1 pF at 10 kHz and a pull-in voltage (Vpull) of 35.6 V, and an open-circuit sensitivity (S0) of 1.62 mV/Pa on a DC bias of 6 V.

A single-pole 6-throw (SP6T) antenna switch using metal-contact RF MEMS switches for multi-band applications

A single-pole 6-throw (SP6T) antenna switch using metal-contact RF micro-electro-mechanical system (MEMS) series switches has been developed for multi-band applications. The fabricated metal-contact MEMS switch with a broad signal line gap of 140 /spl mu/m shows a very high isolation loss of -51 dB at 2 GHz because its center-wedge (CW) can control a membrane stiction problem due to the anchor role. The pull-down voltage (V/sub P/) of the MEMS switch is 27.5 V and its leakage current is 26.1 /spl mu/A at V/sub P/. The SP6T antenna switch, which has six SPST MEMS switches, is comprised of two transmitter (Tx) ports and four receiver (Rx) ports for quad-band application. The chip area is very compact to 1 mm/sup 2/ (1.3 mm /spl times/ 0.8 mm). This antenna switch has an isolation loss of -48 dB and an insertion loss of -0.27 dB at 2 GHz between the antenna (ANT) port and transmitter portl (T/spl times/1) at V/sub A/ = 36V.

A concave-patterned TiN/PECVD-Si3N4 /TiN diaphragm MEMS acoustic sensor based on a polyimide sacrificial layer

In this paper, we present a concave-patterned TiN/PECVD-Si3N4 /TiN diaphragm micro-electro-mechanical system (MEMS) acoustic sensor based on a polyimide sacrificial layer. The use of the spin-coated polyimide eliminates the additional Al pad process of conventional device fabrication due to simple O2 ashing to release the sacrificial layer, simplifying the photolithography process. Also, to adjust the acoustic sensor for a bottom-ported package, its diaphragm was implemented to be placed over the back-plate. The TiN/PECVD-Si3N4/TiN multi-layer diaphragm was formed with the stress controllability of PECVD-Si3N4 from −162 MPa to +109 MPa. Furthermore, a parallel-plate capacitance model on the basis of an approximately linearized electric field method (ALEM) is proposed to evaluate the capacitance of two plates. The modelled capacitance showed less than 3.7% error in FEM simulation, demonstrating the validity of the proposed model. At a zero-bias voltage, the effective intrinsic and parasitic capacitances in the active area were 1.656 pF and 0.388 pF, respectively. Moreover, with a pull-in analytical model by using ALEM, the effective tensile stress for the diaphragm was extracted to +31.5 MPa, where the pull-in voltage was 10.7 V. In succession, the dynamic response for the open-circuit sensitivity was modelled with an equivalent circuit model based on lumped parameters. The measured open-circuit sensitivity of −45.1 dBV Pa−1 at 1 kHz with a bias of 9.6 V was only slightly different from the modelled sensitivity of −45.0 dBV Pa−1. Thus, these results demonstrate that the proposed sensor is suitable for a front-end voice capture module.

A surface-micromachined MEMS acoustic sensor with 0.8 µm CMOS impedance transducer

A surface-micromachined capacitive-type micro-electro-mechanical system (MEMS) acoustic sensor with 0.8 µm CMOS impedance transducer is presented. This sensor chip is composed of a surface-micromachined MEMS microphone with X-shape bottom electrode anchors and a simple monolithic integrated impedance transducer based on 0.8 µm CMOS process (1 poly-2 metals), where Metal 2 in the CMOS process is also used as a bottom electrode for a sensor part. The total chip area is 0.8 mm × 0.9 mm. The Si MEMS acoustic sensor proposed in this paper has a diameter of 500 µm and a back chamber depth of 20 µm. It shows a zero-bias capacitance of 1.25 pF at 1 kHz and a pull down voltage of 33.4 V, and an open-circuit sensitivity of 0.53 mV/Pa on a bias of 9 V. In addition, the impedance transducer transfers a high output impedance to a low input impedance with a 9.5 dB gain at an input condition of 5 mV at 1 kHz.

A bottom-inlet type MEMS acoustic sensor with wheel-shaped back-plate anchor

A bottom-inlet type micro-electro-mechanical system (MEMS) acoustic sensor with a wheel-shaped back-plate anchor is presented. Underneath the back-plate, the wheel-shape anchor is newly inserted to be adjusted to a fixed stator on a substrate. The 30 μm;-high back-plate anchor is patterned by deep reactive-ion etching (DRIE) and covered with a thick back-plate of 2.3 μm; thus, it can play an important role in protecting the foundations under the diaphragm anchors from other loads. Furthermore, structure-based equivalent circuit modeling for a capacitive-type MEMS acoustic sensor is implemented with a lumped model, which is subsequently divided into three main areas: acoustic, mechanical, and electrical domains. The acoustic sensor had an open-circuit sensitivity of -43.0 dBV/Pa at 1 kHz with a bias of 10.0 V, while the modeled open-circuit sensitivity was -42.7 dBV/Pa, which shows good agreement in the range from 100 Hz to 18 kHz. This demonstrates the validity of the structure-based equivalent circuit model for the prediction and design of the sensor.

Structure-based equivalent circuit modeling of a capacitive-type MEMS microphone

Structure-based equivalent circuit modeling for a capacitive-type MEMS acoustic sensor is presented. The model is subsequently divided into three main areas: acoustic, mechanical, and electrical domains. Furthermore, it is composed of three different parameter groups: empirical, theoretical, and mixed data. With an extraction method using measured values, the compliance of a diaphragm and the zero-bias intrinsic capacitance were evaluated to 3.430 × 10-3 m/N and 1.02 pF, respectively, whereas the viscous resistance of acoustic holes and an equivalent mass were calculated to be 2.958 × 108 kg/s·m4 and 7.856 × 10-10 kg, respectively, with theoretical calculation from geological dimension. To verify the proposed model, the open-circuit sensitivities were compared between the modeled and measured values. The MEMS microphone had an open-circuit sensitivity of -48.5 dBV/Pa at 1 kHz with a bias of 10.4 V, while the modeled open-circuit sensitivity was -48.6 dBV/Pa, which shows good agreement in the range from 100 Hz to 18 kHz. That indicates the validation of the structure-based equivalent circuit model to predict and design the MEMS microphone.

Capacitive micro inclinometer with scalloping-free and footing-free vertical electrodes using crystalline etching of (110) silicon

A micromachined capacitive inclinometer has been developed to detect inclination angles for a position sensing application. In order to enhance resolution, a (110) crystalline silicon-on-patterned-insulator (COPI) process has been proposed to remove the morphologic defects such as footing and scalloping which were formed from silicon deep reactive ion etching (DRIE) process. The sidewalls fabricated by the (110) COPI process remarkably became vertical and flat with few nanometer roughness. The micro inclinometer with flat and vertical sensing electrodes was evaluated in terms of capacitance change and detection limit. The capacitance change of the fabricated device is from -0.246 to 0.258 pF for the inclination angle (-90deg to 90deg). The temporal deviation of the capacitance is as small as 0.2 fF, which leads to 0.3 or less resolution for plusmn70deg.