CMOS-MEMS Technology Research Articles

A 3-Axis Miniature Magnetic Sensor Based on a Planar Fluxgate Magnetometer with an Orthogonal Fluxguide.

A new class of tri-axial miniature magnetometer consisting of a planar fluxgate structure with an orthogonal ferromagnetic fluxguide centrally situated over the magnetic cores is presented. The magnetic sensor possesses a cruciform ferromagnetic core placed diagonally upon the square excitation coil under which two pairs of pick-up coils for in-plane field detection are allocated. Effective principles and analysis of the magnetometer for 3-D field vectors are described and verified by numerically electromagnetic simulation for the excitation and magnetization of the ferromagnetic cores. The sensor is operated by applying the second-harmonic detection technique that can verify V-B relationship and device responsivity. Experimental characterization of the miniature fluxgate device demonstrates satisfactory spatial magnetic field detection results in terms of responsivity and noise spectrum. As a result, at an excitation frequency of 50 kHz, a maximum in-plane responsivity of 122.4 V/T appears and a maximum out-of-plane responsivity of 11.6 V/T is obtained as well. The minimum field noise spectra are found to be 0.11 nT/√Hz and 6.29 nT/√Hz, respectively, in X- and Z-axis at 1 Hz under the same excitation frequency. Compared with the previous tri-axis fluxgate devices, this planar magnetic sensor with an orthogonal fluxguide provides beneficial enhancement in both sensory functionality and manufacturing simplicity. More importantly, this novel device concept is considered highly suitable for the extension to a silicon sensor made by the current CMOS-MEMS technologies, thus emphasizing its emerging applications of field detection in portable industrial electronics.

A CMOS micromachined capacitive tactile sensor with integrated readout circuits and compensation of process variations.

This paper presents a capacitive tactile sensor fabricated in a standard CMOS process. Both of the sensor and readout circuits are integrated on a single chip by a TSMC 0.35 μm CMOS MEMS technology. In order to improve the sensitivity, a T-shaped protrusion is proposed and implemented. This sensor comprises the metal layer and the dielectric layer without extra thin film deposition, and can be completed with few post-processing steps. By a nano-indenter, the measured spring constant of the T-shaped structure is 2.19 kNewton/m. Fully differential correlated double sampling capacitor-to-voltage converter (CDS-CVC) and reference capacitor correction are utilized to compensate process variations and improve the accuracy of the readout circuits. The measured displacement-to-voltage transductance is 7.15 mV/nm, and the sensitivity is 3.26 mV/μNewton. The overall power dissipation is 132.8 μW.

High-sensitivity low-noise miniature fluxgate magnetometers using a flip chip conceptual design.

This paper presents a novel class of miniature fluxgate magnetometers fabricated on a print circuit board (PCB) substrate and electrically connected to each other similar to the current “flip chip” concept in semiconductor package. This sensor is soldered together by reversely flipping a 5 cm × 3 cm PCB substrate to the other identical one which includes dual magnetic cores, planar pick-up coils, and 3-D excitation coils constructed by planar Cu interconnections patterned on PCB substrates. Principles and analysis of the fluxgate sensor are introduced first, and followed by FEA electromagnetic modeling and simulation for the proposed sensor. Comprehensive characteristic experiments of the miniature fluxgate device exhibit favorable results in terms of sensitivity (or “responsivity” for magnetometers) and field noise spectrum. The sensor is driven and characterized by employing the improved second-harmonic detection technique that enables linear V-B correlation and responsivity verification. In addition, the double magnitude of responsivity measured under very low frequency (1 Hz) magnetic fields is experimentally demonstrated. As a result, the maximum responsivity of 593 V/T occurs at 50 kHz of excitation frequency with the second harmonic wave of excitation; however, the minimum magnetic field noise is found to be 0.05 nT/Hz1/2 at 1 Hz under the same excitation. In comparison with other miniature planar fluxgates published to date, the fluxgate magnetic sensor with flip chip configuration offers advances in both device functionality and fabrication simplicity. More importantly, the novel design can be further extended to a silicon-based micro-fluxgate chip manufactured by emerging CMOS-MEMS technologies, thus enriching its potential range of applications in modern engineering and the consumer electronics market.

Integrated CMOS-MEMS Technology and Its Applications

Fusion of microelectromechanical systems (MEMS) with CMOS LSI technologies is a promising way to develop high functional devices. We have been developing the integrated CMOS-MEMS technology that fabricates MEMS devices on CMOS LSI[1-2]. Thetechnology has the features ofhigh-functionality, high-accuracy, and mass-production.In this paper, first, MEMS technology trends and the concept of the integrated CMOS-MEMS technology are described. Next, we present the multi-physics simulation for the CMOS-MEMS technology[3-4]. Finally, as the examples, we demonstrate the arrayed CMOS-MEMS accelerometer[5-7].Prospects and challenges of the integrated CMOS-MEMS technology are described from the view point of CMOS-LSI (Fig.1). It indicates that this technology gives the solution of developing high functional devices.We have developed the multi-physics simulation platform to analyze the electromechanical behaviors of MEMS and CMOS simultaneously. Based on the analytical model, the equivalent circuit was proposed to simulate the above behavior on a Verilog-A compatible hardware description language (Fig.2).Small size and wide range accelerometers are increasingly in demand in the various system. Figure 3 shows the proposed arrayed CMOS-MEMS accelerometer that was capable of detecting a wide range of acceleration. The MEMS accelerometer was fabricated by gold electroplating with post-CMOS process. We can obtain the 3-by-3 arrayed MEMS accelerometer with the sensing range from 1.7G to 20G(Fig. 4). Also, using the simulation results obtained by the above multi-physics platform, we can realize the CMOS-MEMS accelerometer.In conclusion, it is confirmed that the integrated CMOS-MEMS technology will pave the way for the More than Moore technology.

A capacitive CMOS–MEMS sensor designed by multi-physics simulation for integrated CMOS–MEMS technology

This paper reports the design and evaluation results of a capacitive CMOS–MEMS sensor that consists of the proposed sensor circuit and a capacitive MEMS device implemented on the circuit. To design a capacitive CMOS–MEMS sensor, a multi-physics simulation of the electromechanical behavior of both the MEMS structure and the sensing LSI was carried out simultaneously. In order to verify the validity of the design, we applied the capacitive CMOS–MEMS sensor to a MEMS accelerometer implemented by the post-CMOS process onto a 0.35-µm CMOS circuit. The experimental results of the CMOS–MEMS accelerometer exhibited good agreement with the simulation results within the input acceleration range between 0.5 and 6 G (1 G = 9.8 m/s2), corresponding to the output voltages between 908.6 and 915.4 mV, respectively. Therefore, we have confirmed that our capacitive CMOS–MEMS sensor and the multi-physics simulation will be beneficial method to realize integrated CMOS–MEMS technology.

Integrated CMOS-MEMS Technology and Its Applications

The paper reports a feature and techniques to resolve requirements of integrated CMOS-MEMS technology. The multiphysics simulation platform for this technology has been developed to understand simultaneously both the mechanical and electrical behaviors of MEMS stacked on LSI. An equivalent circuit of a MEMS accelerometer has been developed with an electrical circuit simulator. We review the technology for CMOS-MEMS accelerometer with a wide detection range. Using the simulation platform above, we investigated the capacitive CMOS-MEMS sensor to a MEMS accelerometer implemented by the post-CMOS process onto CMOS circuit. As a result, it is confirmed that integrated CMOS-MEMS technology will shed light on a solution of More than Moore technical trends.

An arrayed accelerometer device of a wide range of detection for integrated CMOS–MEMS technology

This paper reports the design and experimental results of an arrayed accelerometer device in 3 × 3 format that can detect wide range of acceleration between 1G and 20G (1G = 9.8 m/s2). Implemented in a single chip has been performed by gold electroplating for integrated complementary metal oxide semiconductor–microelectromechanical systems (CMOS–MEMS) technology. An equivalent circuit of a MEMS accelerometer has been developed with an electrical circuit simulator to demonstrate the mixed-behavior of the arrayed sensor device and sensing CMOS circuits. Mechanical and electrical crosstalk between the arrayed elements is analyzed on the electrical field distributions. Experimental results show that the resonant frequency and readout capacitance as a function of applied acceleration have been well explained by the results of the multi-physics simulation. As a result, it is confirmed that the proposed device is applicable to an integrated CMOS–MEMS arrayed accelerometer.

A 3D FEM Model for Heat Transfer Mechanisms in Membrane Based Thermal Conductivity Sensors Developed Using SOI CMOS MEMS Technology

© 2014 Published by Elsevier Ltd. This paper presents an experimentally verified 3D FEM model to understand heat transfer mechanisms in membrane based thermal conductivity sensors developed using SOI CMOS MEMS technology. It aims to provide a structured methodology to design micro thermal conductivity sensors for gas detection. The reported model takes in to account heat transfer by conduction and convection in conjunction with device geometry and is based on a sensor fabricated at a commercial CMOS foundry using a 1 μm process that measures only 1 × 1 mm2.

CMOS-MEMS Integration in Micro Fabry Perot Pressure Sensor Fabrication

Integration of Complimentary Metal-Oxide-Semiconductor (CMOS) and Microelectromechanical System (MEMS) technology in Fabry Perot blood pressure sensor (FPPS) fabrication processes is presented. The sensor that comprises of a 125 µm diameter of circular diaphragm is modeled to be fabricated using integration of CMOS-MEMS technology. To improve the sensor reliability, a sleeve structure is designed at the back of Silicon wafer by using MEMS Deep Reactive ion Etching (DRIE) process for fiber insertion, which offers a large bonding area. Optical light source at 550 nm wavelength is chosen for this device. The sensor diaphragm mechanic deflection and its optical spectrum is theoretically analyzed and simulated. The analytical results show high linear response in the range of 0 to 40 kPa and a reasonable sensitivity of 1.83 nm/kPa (spectrum shift/pressure) has been obtained for this sensor. The proposed integration of CMOS-MEMS technology limit the material selection yet produces an economical method of FPPS fabrication and integrated system.

A V-Band Three-State Phase Shifter in CMOS-MEMS Technology

A V-band CMOS-MEMS switchable phase shifter based on reflection-type topology is presented in this work. The phase shifter is fabricated in 0.18- $\mu{\rm m}$ CMOS process with a chip size of 1.04 ${\rm mm}^{2}$ , wherein the suspended MEMS structure is released through the post-CMOS micromachining. Three discrete phase states, including 0 $^{\circ}$ , 89 $^{\circ}$ , 144 $^{\circ}$ at 65 GHz, can be achieved by the bi-directional fishbone actuators under 46-V actuation voltage. The measured insertion loss is $2.2\pm 1~{\rm dB}$ and the return loss is better than 14 dB over the 55–65 GHz frequency range, demonstrating a great potential in many applications.

Analogy among microfluidics, micromechanics, and microelectronics

We wish to illuminate the analogous link between microfluidic-based devices, and the already established pairing of micromechanics and microelectronics to create a triangular/three-way scientific relationship as a means of interlinking familial disciplines and accomplishing two primary goals: (1) to facilitate the modeling of multidisciplinary domains; and, (2) to enable us to co-simulate the entire system within a compact circuit simulator (e.g., Cadence or SPICE). A microfluidic channel-like structure embedded in a micro-electro-mechanical resonator via our proposed CMOS-MEMS technology is used to illustrate the connections among microfluidics, micromechanics, and microelectronics.

Realizing Deep-Submicron Gap Spacing for CMOS-MEMS Resonators

Integrated complementary metal-oxide-semiconductor (CMOS)-microelectro mechanical systems (MEMS) beam-array resonators that take advantage of the pull-in effect to surmount limitations of standard CMOS foundry processes have been demonstrated to attain electrode-to-resonator gap spacing at a deep-submicrometer range. Such deep-submicrometer gaps lead to much larger electromechanical coupling coefficient and smaller motional impedance as compared with conventional CMOS-MEMS technologies. In addition, a unique frequency tuning capability by modulating the mechanical boundary conditions (“BC”) of the resonators has also been proposed. Furthermore, the mechanically coupled array approach used in this paper not only provides five times smaller motional impedance compared with that of a single resonator but offers superior power handling capability due to higher stiffness of the arrayed resonator. In such an array design, high velocity coupling for beam-array resonators effects a single resonance behavior without spurious modes. With the increase of an applied dc-bias which simultaneously serves for functions of pull-in and resonator operation, the upward frequency shift of resonance caused by boundary condition change offers opposite tuning mechanism against the well-known effect of electrical stiffness. As a result, frequency variation induced by the BC-modulation and electrical stiffness would yield a frequency-insensitive region under a certain dc-bias voltage. Furthermore, the use of metal/oxide composite materials for resonator structures in this paper substantially alleviates residual stress often seen in the CMOS layers as compared to mere-metal resonators.

Fabrication and Characteristics of an nc-Si/c-Si Heterojunction MOSFETs Pressure Sensor

A novel nc-Si/c-Si heterojunction MOSFETs pressure sensor is proposed in this paper, with four p-MOSFETs with nc-Si/c-Si heterojunction as source and drain. The four p-MOSFETs are designed and fabricated on a square silicon membrane by CMOS process and MEMS technology where channel resistances of the four nc-Si/c-Si heterojunction MOSFETs form a Wheatstone bridge. When the additional pressure is P, the nc-Si/c-Si heterojunction MOSFETs pressure sensor can measure this additional pressure P. The experimental results show that when the supply voltage is 3 V, length-width (L:W) ratio is 2:1, and the silicon membrane thickness is 75 μm, the full scale output voltage of the pressure sensor is 15.50 mV at room temperature, and pressure sensitivity is 0.097 mV/kPa. When the supply voltage and L:W ratio are the same as the above, and the silicon membrane thickness is 45 μm, the full scale output voltage is 43.05 mV, and pressure sensitivity is 2.153 mV/kPa. Therefore, the sensor has higher sensitivity and good temperature characteristics compared to the traditional piezoresistive pressure sensor.

(Invited) From MEMS-CMOS towards Heterogeneous Integration over Scale

Micromachining technology has created a great variety of micro/nanoelectromechanical systems (MEMS/NEMS) through the integration of moving mechanisms, sensors, and electronics in a chip-size system. Integration of CMOS circuitry and MEMS technology improves the performance of micro sensors and actuators, programmability, miniaturization and simplicity of total device packaging. It is expected that MEMS-CMOS technology enables a more-than-Moore solution for the next-generation electronics. Such heterogeneous integration will be expanded over scale and material. Organic and inorganic chemistry as well as bio technology can provide functional materials for sensing, energy conversion and actuation. Printing can be an inexpensive way to have micro patterns on a meter-size substrate or film. The concept and examples of heterogeneous integration are discussed.

Using a Floating-Gate MOS Transistor as a Transducer in a MEMS Gas Sensing System

Floating-gate MOS transistors have been widely used in diverse analog and digital applications. One of these is as a charge sensitive device in sensors for pH measurement in solutions or using gates with metals like Pd or Pt for hydrogen sensing. Efforts are being made to monolithically integrate sensors together with controlling and signal processing electronics using standard technologies. This can be achieved with the demonstrated compatibility between available CMOS technology and MEMS technology. In this paper an in-depth analysis is done regarding the reliability of floating-gate MOS transistors when charge produced by a chemical reaction between metallic oxide thin films with either reducing or oxidizing gases is present. These chemical reactions need temperatures around 200 °C or higher to take place, so thermal insulation of the sensing area must be assured for appropriate operation of the electronics at room temperature. The operation principle of the proposal here presented is confirmed by connecting the gate of a conventional MOS transistor in series with a Fe2O3 layer. It is shown that an electrochemical potential is present on the ferrite layer when reacting with propane.