Post-CMOS processing for high-aspect-ratio integrated silicon microstructures (original) (raw)
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Design and Modeling of Silicon MEMS Accelerometer
irep.iium.edu.my
In developing Micro Electro Mechanical Systems (MEMS), Finite Element Analysis (FEA) is usually relied upon to study these micro-structures in determining stress, deformation, resonance, temperature distribution, electromagnetic interference, and electrical properties. With this kind of approach, the performance of the devices can be easily expanded, as well as reducing the time and cost of MEMS production. This paper focuses on the modeling of silicon MEMS accelerometer in an attempt to design a surface micro-machined accelerometer that satisfies certain pre-determined specifications.
Micro-G silicon accelerometer using surface electrodes
2009
We present a new technology platform for silicon inertial sensors. The platform combines three technology features to set new performance and manufacturability standards for MEMS sensors. First, bonding three silicon wafers creates wafer level packaging and a homogenous stack of silicon material improving device temperature stability. Second, through-wafer etching is used to define the mechanical structure creating a proof mass with 1000x larger mass than a typical MEMS sensor. Finally, we use surface electrode technology to create a lateral capacitance-based transducer enabling large capacitance change per acceleration and allowing a large dynamic range without electrode contact. The large mass together with reduced damping of a lateral sensor result in substantially reduced thermal-mechanical noise. We present a two axis, in-plane, MEMS accelerometer having nG/√Hz noise performance, over 130 dB dynamic range, 300 Hz bandwidth, and a chip size comparable to other MEMS accelerometers. The platform is extensible to gyroscopes and single chip IMU. I.
Low-g Area-changed MEMS Accelerometer Using Bulk Silicon Technique
American Journal of Applied Sciences, 2008
A bulk micromachined accelerometer based on an area variation capacitive sensing for low-g applications was developed. The accelerometer was designed with ribbed-style fingers structure on the movable mass connected in parallel and suspended over stationary electrodes composed of differential comb fingers by means of suspension beams anchored onto the substrate. A folded, rigid truss suspension design with low spring constant and low cross-axis sensitivity was chosen. The simulation was performed using Coventorware software. A threemask bulk micromachining wafer bonding fabrication process was utilized to realize the accelerometer. Silicon-on-glass was used to achieve high sensitivity and low mechanical noise while maintaining a simple structure. The general concept, main design considerations, fabrication procedure and performance of the resulted accelerometer was elaborated and presented. A linear relationship between the differential capacitance and acceleration was obtained. The accelerometer sensitivity was calculated to be 0.47 pF/g with an acceleration range of ±5 g.
A novel high aspect ratio technology for MEMS fabrication using standard silicon wafers
Sensors and Actuators A: Physical, 2002
This paper presents a novel MEMS fabrication technology based on standard single crystal silicon wafers. High aspect ratio structures are manufactured using a three mask level technology and dry processing throughout. The complete process¯ow is presented and a discussion of the most critical process steps is given. After processing the released micromechanical components consist of mono-crystalline silicon without additional thin ®lms. In contrast to other solutions only one release etch step is necessary. The micromechanical components are ®xed with anchor like structures. As a result of the novel process¯ow these anchors are surrounded by air gaps. Thus a strongly reduced parasitic capacitance with respect to bulk silicon is achieved. These air gap insulated microstructures (AIM) were fabricated and tested with respect to mechanical stability, temperature dependence and electrical behaviour of an exemplary oscillator structure. #
Microelectronics Journal, 2006
The CMOS compatible bulk micromachined piezoresistive accelerometer presented in this paper consists of four flexures supporting a proof mass. Four pairs of boron-diffused piezoresistors are located at maximum stress points on the flexures near the proof mass and frame ends. Because of the opposite nature of stress at the two ends, these piezoresistors can be connected to form a Wheatstone bridge such that the off-axis responses are practically cancelled while the on-axis (along perpendicular to proof mass) response is maximized. The device is simulated using CoventorWare. In the fabrication process, dual-doped TMAH solution is used for wet anisotropic etching. The novelty of this etching process is that the bulk micromachining can be performed after aluminum metallization. The etched surface is also smooth. The fabrication is thus CMOS compatible. The accelerometer exhibits good linearity over 0-10 g.
Static mechanical analysis of a silicon bulk-micromachined accelerometer
This work describes a static mechanical analysis of a microaccelerometer. This accelerometer is fabricated by bulk micromachining of silicon in KOH solution. The mechanical part of this device consists of an inertial mass suspended by four silicon beams fixed at the edges. The calculation of the equivalent spring constant is done using basic solid mechanics theory. Both large and small deflections cases are analyzed in this study. We determined the Young's modulus and Poisson's ratio according to the crystallographic orientation of the silicon beams. The calculation of the mass and the second moment of area is evaluated taking into account the hexagonal cross section formed during the bulk-micromachined process. The maximum normal stress failure criteria is utilized to determine the maximum stress in the mechanical structure for a given load. The effective mass of the system is calculated discussing the influence of the mass of the beams in the natural frequency and in the static sensitivity of the system. The validity of the model is discussed according to the assumptions and simplifications made. Finally, all analytical results are compared with the ones obtained by the finite element method (FEM). The results show a good agreement between the two methods, validating the analytical model for this kind of analysis.
Silicon resonant accelerometer with electronic compensation of input-output cross-talk
Sensors and Actuators A: Physical, 2005
A resonant accelerometer manufactured in silicon bulk micromachining with electrothermal excitation and piezoresistive detection is presented. The structure is a seismic mass supported by two parallel flexure hinges as a doubly-sustained cantilever, with a resonating microbeam located between the hinges. The acceleration normal to the chip plane induces an axial stress in the microbeam and, in turn, a proportional change in the microbeam resonant frequency. Beam resonant frequency of around 70 kHz and acceleration sensitivity of 35 Hz/g over the range 0-3 kHz were measured on prototypes, in accordance with analytical calculations and simulations. The microbeam operates unsealed at atmospheric pressure, therefore a comparatively low quality factor results due to air damping. In this condition, the effect of the input-output cross-talk was found to be significant. The cross-talk is analyzed and modeled, and an electronic active compensation is proposed. The compensated sensor was inserted into a phase-locked loop oscillator and tested. Reported experimental results show that the sensor performs in excellent agreement with the theoretical predictions.
A low-cost micromechanical accelerometer with integrated solid-state sensor
Sensors and Actuators A: Physical, 2000
Accelerometers are probably the most common application of MEMS technology as they only require sensing the movement of a mass subject to acceleration. Still, because of the irrelatively high cost, the potential of accelerometers is not fully utilized. This paper discusses Ž. the performance of the Direct Integration DI of stress sensors made of pn diodes and MOS transistors with Micromachined accelerometer. The accelerometers are made of beam with cross-section of 2 mm = 20 mm connected to proof mass. The stress sensors are fabricated at the root of the beam and respond to stress developed as a result of mechanical excitation. This stress modulates the silicon band gap energy and thus affects the I-V transfer function of the sensor. The sensors and the supporting ICs are fabricated by a Ž conventional micro fabrication facility and the mechanical part is fabricated subsequently, using SCREAM Single Crystal Reactive Ion. Etching and Metallization process that adds only one lithography step to the IC's lithography steps. This low-cost integration may reduce the cost of accelerometers and increase their potential use.
Silicon Microminiature Low-Frequency Accelerometer
Works of the Moscow Forestry Engineering Institute. (In Russian), 1985
The exponential growth in demand for compact and efficient accelerometers is driven by their diverse applications across industries such as automotive, aerospace, consumer electronics, and healthcare. This article presents two designs of small-size accelerometers: the ultra-compact "SRAmicro" and the slightly larger, higher-accuracy "SRAHi−P re." Both accelerometers are designed to operate in frequency ranges of (0 ÷ 200) Hz and temperatures −50◦C − +180◦C. The SRAmicro model is ideal for applications with limited space, while the SRAHi−Pre model offers higher accuracy for mission-critical applications. The article discusses the structures, materials, and methods used to create and optimize these accelerometers. Experimental results indicate that the SRAHi−Pre model, when combined with a thermal compensation circuit, significantly reduces the temperature sensitivity parameter (γ) and improves the overall performance of the device. These compact accelerometers have the potential to meet the increasing demands for diverse applications in various industries.