Complementary Metal Oxide Semiconductor Microelectromechanical Systems Research Articles

Monolithic Integration of Gesn on Si for IR Camera Demonstration

Due to the development of cost-efficient detector technologies in the NIR (Near Infrared), new areas of application are constantly being addressed. This affects autonomous driving, where LiDAR (Light Detection and Ranging) systems with better eye safety are being developed, as well as low-cost night vision cameras. Another area of application is NIR spectroscopy, e.g. in the areas of food monitoring, environmental research or medical technology. The increasing need for portable, low-cost analysis devices, for example for "on-site" measurements or for everyday life, is driving the development of highly miniaturized and low-cost lab-on-a-chip systems. The NIR detectors and NIR cameras available on the market are primarily based on materials from group III/V compound semiconductors, e.g. InGaAs. However, the CMOS (Complementary Metal Oxide Semiconductor) standard process cannot be used for the production of this technology, which significantly increases the cost factor and thus limits its use on the market. A promising alternative is offered by group IV based detectors, in particular Ge and GeSn detectors, which can be monolithically integrated on a Si substrate. As a result, such detector systems can be processed much more cost-efficiently with CMOS compatible standard technology. The NIR absorption properties are also comparable to III/V components.This paper reports on the monolithic integration of Ge and GeSn detector arrays on Si substrates for the realization of a camera system. The entire system consists of a photonic chip, a readout chip and a standard microcontroller, which is connected to a laptop via USB. The SNR (signal-to-noise ratio) is an important parameter for such an integrated system. The quantum efficiency of each individual pixel sensor has to be maximized and a high fill factor per pixel is aimed for. A particularly high fill factor is achieved here with optical light coupling via the substrate back-side, since the front-side metallization does not interfere with the optical coupling area. Furthermore, the metallization acts then as a mirror, the light thus passes through the absorption area twice and leads to a higher quantum efficiency.However, the main obstacle of Ge and GeSn, compared to III/V devices, is the higher intrinsic charge carrier concentration, which leads to a significantly higher dark current. A possible solution is the zero bias operation of the detector at the expected dark current minimum. The dark current is 3 orders of magnitude smaller at 0 V compared to an operating point at -1 V. Another criterion for the circuit is that a signal range or photocurrent supports a wide dynamic range (between nA and µA). For this purpose, the photocurrent is fed into the evaluation electronics via a triple cascaded current mirror. The measured value is output to a 12-bit ADC (Analog Digital Converter) integrated in the microcontroller via a current/voltage converter, two buffers and a sample hold element. With the help of additional multiplexers, the circuit can be used to read out several detectors and thus address a pixel matrix.We report on the fabrication of the photonic chip, which is carried out using CMOS compatible processes and MEMS (Micro-Electro-Mechanical System) processes in combination with an epitaxial growth of the active device structures. The photonic chip is based on 150 mm Si substrates, which were prepared first with multiple ion implantation steps. The active pin detector layers, consisting of Si and Ge or GeSn, were grown by means of molecular beam epitaxy. Afterwards, deep trenches were now etched between the detectors in a MEMS process to minimize crosstalk between neighboring pixels. The detectors were structured then using CMOS processes, and the backside is polished or structured. Finally, a two layer frontside-metallization is applied for the contacts. We demonstrate the functionality of both two-dimensional and linear detector arrays and show possible applications such as NIR cameras or NIR spectrometers.

Hybrid Microfluxgate and Current Transformer Sensor

In this work, we develop the hybrid current sensor comprising a microfluxgate and a current transformer (CT) for wide-bandwidth current measurement. The microfluxgate consists of two microcoil chips 3.5 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times1.75$ </tex-math></inline-formula> mm in dimension made by using the standard Complementary Metal-Oxide Semiconductor MicroElectroMechanical Systems (CMOS-MEMS) <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.35 ~\mu \text{m}$ </tex-math></inline-formula> process. The aluminum wire-bonding technique is used to construct the top excitation coil surrounding the amorphous soft magnetic core patterned by photolithography and wet etching techniques. Under the optimal excitation condition, the response of the microfluxgate current sensor becomes linear with a maximized sensitivity. The in-house made CT is combined with the microfluxgate driving system to form the hybrid current sensor by using a summing amplifier. The hybrid current sensor has a spectral current noise of 0.4 mA/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\surd $ </tex-math></inline-formula> Hz at 1 Hz. The maximum sensing range is ±10 A, and the non-linearity is less than 2% within the ±4.6 A range, corresponding to a linear dynamic range of 60 dB in a 10 Hz bandwidth. The hybrid microfluxgate-and-CT sensor has a flat bandwidth from dc to 100 kHz. It has the potential to become a practical miniature device featuring a high-dynamic range, wide bandwidth, and low-temperature drift.

Foundry Service of CMOS MEMS Processes and the Case Study of the Flow Sensor

The complementary metal-oxide-semiconductor (CMOS) process is the main stream to fabricate integrated circuits (ICs) in the semiconductor industry. Microelectromechanical systems (MEMS), when combined with CMOS electronics to form the CMOS MEMS process, have the merits of small features, low power consumption, on-chip circuitry, and high sensitivity to develop microsensors and micro actuators. Firstly, the authors review the educational CMOS MEMS foundry service provided by the Taiwan Semiconductor Research Institute (TSRI) allied with the United Microelectronics Corporation (UMC) and the Taiwan Semiconductor Manufacturing Company (TSMC). Taiwan’s foundry service of ICs is leading in the world. Secondly, the authors show the new flow sensor integrated with an instrumentation amplifier (IA) fabricated by the latest UMC 0.18 µm CMOS MEMS process as the case study. The new flow sensor adopted the self-heating resistive-thermal-detector (RTD) to sense the flow speed. This self-heating RTD half-bridge alone gives a normalized output sensitivity of 138 µV/V/(m/s)/mW only. After being integrated with an on-chip amplifier gain of 20 dB, the overall sensitivity of the flow sensor was measured and substantially improved to 1388 µV/V/(m/s)/mW for the flow speed range of 0–5 m/s. Finally, the advantages of the CMOS MEMS flow sensors are justified and discussed by the testing results.

A Nanoscale Hot-Wire Flow Sensor Based on CMOS-MEMS Technology

In this paper, we proposed an ultrafast and nanoscale hot-wire flow (NHF) sensor implemented in a 0.18 µm complementary metal-oxide-semiconductor microelectromechanical system (CMOS-MEMS) technology. The nanoscale wire was released and reduced in thickness and width by an in-house developed post-CMOS fabrication process, hence the heat conduction loss is greatly suppressed, while the response time of the NHF sensor is significantly improved. Benefiting from the nano size of the hot-wire (a width of 622 nm), the NHF sensor exhibits an ultrafast response time of 30 µs (@ airflow velocity of 0 m/s), a wide flow range of 0–30 m/s, and a cut-off frequency of 21 kHz under the constant temperature (CT) mode. In addition, an equivalent circuit model (ECM) was established in PSPICE to predict the NHF sensor performance, and the theoretical simulation results were in good agreement with the experiment results.

Bidirectional CMOS-MEMS Airflow Sensor With Sub-mW Power Consumption and High Sensitivity

This article presents a bidirectional thermoresistive micro calorimetric flow (TMCF) sensor implemented by a 0.18- <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">μ</i> m complementary metal–oxide–semiconductor microelectromechanical systems (CMOS-MEMS) technology, while the sensor thickness is thinned to 2.7 μm through an in-house developed MEMS fabrication process. For the bidirectional airflow of −6 to 6 m/s, the TMCF sensor achieves the highest sensitivity of 453 mV/(m/s), and its highest normalized sensitivity with respect to the signal amplification gain (gain = 250) and the input heating power (1.58–1.72 mW) is 1150 mV/(m/s)/W. By reducing the heating power to the sub-mW of <220 μW, the TMCF sensor can still give a remarkable sensitivity of 87.4 mV/(m/s). In addition, the developed TMCF sensor has an intrinsic minimum detectable flow velocity of 99 μm/s and a response time of 4.8 ms. The performance achieved by this flow sensor enables accurate indoor airflow measurements even when dealing with the extremely low-speed flow (<0.05 m/s). Furthermore, the high-performance TMCF sensor is applied for remote human motion detection, where different walking speeds and moving patterns of the occupants can be captured. Therefore, this developed CMOS-MEMS sensor will not only be a promising flow sensing node in the HVAC system, but also potentially be used for the nonvisible and private occupant counting in buildings/rooms.

Materials Selection Approaches and Fabrication Methods in RF MEMS Switches

A state of the art review on Radio Frequency Micro-Electromechanical Systems (RF MEMS) capacitive switches is reported by considering two key aspects: (1) materials selection approaches for improving performance, and (2) fabrication methods used in capacitive MEMS switches. The beam and dielectric materials used in capacitive MEMS switches and the performance achieved through them are reviewed and reported by a rigorous literature survey. Further, materials selection approaches for the beam membrane and the dielectric layer are discussed using Ashby’s methodology, and other associated methods based on it, which uses material indices to evaluate the performance of a switch. Performance indicators for the beam materials selection are the pull-in voltage, RF loss, thermal residual stress, contact resistance, thermal conductivity, and maximum displacement, whereas the hold-down voltage, dielectric charging, leakage current, heat dissipation, capacitance ratio, and stability are performance indicators in dielectric materials selection. MEMS switch fabrication can be achieved through bulk micromachining processes and surface micromachining processes, but the surface micromachining process has been preferred over the last few decades. The fabricated MEMS switch components can be integrated using a monolithic complementary metal oxide semiconductor–micro-electromechanical systems (CMOS-MEMS) process for the realization of applications in sensors, resonators, amplifiers, phase shifters, and MEMS satellite vehicles for space applications. CMOS-MEMS monolithic fabrication is discussed further with the help of fabrication process involved and the process technology. The TSMC-CMOS 0.35 $$\upmu \hbox {m}$$ technology is one of the leading technologies in CMOS-MEMS fabrication and is mainly used.

A functional CMOS compatible MEMS pyroelectric detector using 12%-doped scandium aluminum nitride

In this paper, we fabricate and demonstrate a functional complementary metal-oxide-semiconductor (CMOS) compatible pyroelectric uncooled thermal detector using 12% doped Scandium Aluminum Nitride (ScAlN) as the sensing layer. The ScAlN pyroelectric material is deposited at a temperature of ∼200 °C over an 8-in. wafer area. This detector has shown, in general, improved performance compared to AlN, with specific detectivity as high as ∼ 6.08×107 cm Hz/W and noise equivalent power as low as ∼ 8.85×10−10 W/Hz. The results show the specific detectivity of ScAlN-based pyroelectric detectors in the range of 107 cm Hz/W, which is an improvement compared to AlN-based pyroelectric detectors which report specific detectivity typically in the range of 105–106 cm Hz/W. This promising result opens up the opportunities for a CMOS compatible, 8-in. wafer-level manufacturable lead-free pyroelectric detector toward low cost and high throughput, allowing microelectromechanical systems (MEMS) and CMOS integration for increased applications in CMOS–MEMS integrated devices utilizing pyroelectric detectors.

Determination of Thermal Conductivities for Thin-Film Materials in CMOS MEMS Process

The determination of thermal conductivities for complementary metal-oxide-semiconductor (CMOS) thin-film materials is very important as the operation and failure of integrated circuits (ICs) and CMOS microelectromechanical systems (MEMS) devices are most likely limited by thermal issues, that is, heat transfer. In this article, we present four micro thermal conductivity measurement (μTCM) devices for silicon oxide, polysilicon, and aluminum thin films using CMOS MEMS technology. To determine the thermal conductivities of those thin-film materials from the μTCM devices, a linear thermal resistance model was proposed and validated by the computational fluid dynamics (CFD) study, which showed an error of less than 5.5%. The thermal conductivities of thin-film materials were then measured over a temperature range of 210-362 K, while the measured results for silicon oxide, polysilicon, and aluminum at room temperature were 1.32, 21.22, and 70.2 W/mK, respectively. Those measured thermal conductivities were significantly smaller than the available bulk values. The discrepancies between the thin film and bulk materials are consistent with the reported data and trends, which reveals the importance of determining the thermal conductivities for thin-film materials in the CMOS MEMS process.

A High-Efficiency Driver Circuit for a Gas-Sensor Microheater Based on a Switch-Mode DC-to-DC Converter.

Low power consumption is one of the critical factors for successful Internet of Things (IoT) applications. In such applications, gas sensors have become a main source of power consumption because energy conversion efficiency of the microheater is relative over a wide range of operating temperatures. To improve the energy-conversion efficiency of gas-sensor microheaters, this paper proposes integrated switch-mode DC-to-DC power converter technology which we compare with traditional driving methods such as pulse-width modulation and the linear mode. The results indicate that energy conversion efficiency with this proposed method remains over 90% from 150 °C to 400 °C when using a 3.0, 4.2 and 5.0 V power supply. Energy-conversion efficiency increases by 1–74% compared with results obtained using the traditional driving methods, and the sensing film still detects alcohol and toluene at 200 °C and 280 °C, respectively, with high energy conversion efficiency. These results show that the proposed method is useful and should be further developed to drive gas-sensor microheaters, and then integrated into the circuits of the complementary metal-oxide-semiconductor micro electro mechanical systems (CMOS-MEMS).

Low-Concentration Ammonia Gas Sensors Manufactured Using the CMOS-MEMS Technique.

This study describes the fabrication of an ammonia gas sensor (AGS) using a complementary metal oxide semiconductor (CMOS)–microelectromechanical system (MEMS) technique. The structure of the AGS features interdigitated electrodes (IDEs) and a sensing material on a silicon substrate. The IDEs are the stacked aluminum layers that are made using the CMOS process. The sensing material; polypyrrole/reduced graphene oxide (PPy/RGO), is synthesized using the oxidation–reduction method; and the material is characterized using an electron spectroscope for chemical analysis (ESCA), a scanning electron microscope (SEM), and high-resolution X-ray diffraction (XRD). After the CMOS process; the AGS needs post-processing to etch an oxide layer and to deposit the sensing material. The resistance of the AGS changes when it is exposed to ammonia. A non-inverting amplifier circuit converts the resistance of the AGS into a voltage signal. The AGS operates at room temperature. Experiments show that the AGS response is 4.5% at a concentration of 1 ppm NH3; and it exhibits good repeatability. The lowest concentration that the AGS can detect is 0.1 ppm NH3

A Robust Fully-Integrated Digital-Output Inductive CMOS-MEMS Accelerometer with Improved Inductor Quality Factor

This paper presents the design, fabrication, and characterization of an inductive complementary metal oxide semiconductor micro-electromechanical systems (CMOS-MEMS) accelerometer with on-chip digital output based on LC oscillators. While most MEMS accelerometers employ capacitive detection schemes, the proposed inductive detection scheme is less susceptible to the stress-induced structural curling and deformation that are commonly seen in CMOS-MEMS devices. Oscillator-based frequency readout does not need analog to digital conversion and thus can simplify the overall system design. In this paper, a high-Q CMOS inductor was connected in series with the low-Q MEMS sensing inductor to improve its quality factor. Measurement results showed the proposed device had an offset frequency of 85.5 MHz, sensitivity of 41.6 kHz/g, noise floor of 8.2 mg/√Hz, bias instability of 0.94 kHz (11 ppm) at an average time of 2.16 s, and nonlinearity of 1.5% full-scale.

Temperature-compensated CMOS-MEMS resonators via electrical stiffness frequency pulling

A passively temperature-compensated micromechanical resonator based on an electrical stiffness frequency pulling technique was demonstrated. In particular, a 2.92 MHz free–free beam resonator achieved by a 0.35 µm 2-poly-4-metal complementary metal-oxide semiconductor microelectromechanical systems (CMOS-MEMS) process platform yields a nearly zero first-order temperature coefficient of frequency (TCF1), from −69.78 ppm °C−1 of an uncompensated version to +0.43 ppm °C−1, and a 12× lower overall frequency drift from the uncompensated 5885 ppm to 496 ppm between 0 °C and 85 °C. The electrical stiffness compensation technique previously demonstrated on a CMOS-incompatible poly-Si surface micromachining process consumes no dc power consumption in contrast to other active methods. In this work, an improved design of the in-plane U-shaped compensating electrode allows not only the employment by a standard CMOS process but also layout-defined temperature dependency of the electrical stiffness via varying the length of the compensating electrode. A theoretical model predicts the thermally induced extension of the compensating electrode and further leads to an optimum electrode length which allows the use of only one voltage source for both compensation and polarization bias voltages. The measured results are compared with the analytical model prediction and discussion on the effects of process induced device parameter variations is presented.

A CMOS-Integrated MEMS Platform for Frequency Stable Resonators-Part I: Fabrication, Implementation, and Characterization

This paper introduces the comprehensive design concepts, procedure, and post-process flow of a robust manufacturing platform for complementary metal-oxide- semiconductor microelectromechanical systems (CMOS-MEMS) resonant transducers with enhanced frequency stability and capacitive-transduction efficiency. Thanks to a sandwich-stacking configuration of the interconnection metal line (TiN/AlCu/TiN) existing in standard CMOS technology, a deep-submicron TiN-to- TiN gap is successfully demonstrated by removing the central AlCu alloy layer through the proposed post-fabrication platform, thus realizing a novel titanium nitride composite (TiN-C) structure. Compared with the traditional release approaches utilized in the general post-CMOS fabrication, the proposed TiN composite transducer with TiN-to-TiN gap can simultaneously attain (i) a 400nm air gap for effective electrostatic transduction, (ii) adequate material selection and arrangement for near-zero frequencytemperature coefficient, and (iii) conductive electrodes to overcome frequency drift induced by dielectric charging during capacitive operation. In Part I of this study, the design guideline, layout rules, and detailed post-fabrication flow are addressed. The fabrication results of each post-process step are also exhibited. Numerical analysis, experiment results, and further discussions in terms of frequency stability for resonant transducers will be covered in Part II. [2018-0230]

Thin-Film MOSFET-Based Pressure Sensor

This paper proposes a silicon-on-insulator (SOI) complementary metal-oxide semiconductor (CMOS) micro-electromechanical system (MEMS) thin-film pressure sensor in which the sensing elements are based on stress sensitive MOSFETs, and the carrier mobility and channel resistance vary with applied pressure. Four MOSFETs are embedded within a silicon dioxide membrane to form a Wheatstone bridge. The sensors are fabricated in a commercial foundry with p-channel and n-channel designs both investigated. The fabricated pMOSFET design gave a pressure sensitivity of 5.21 mV/kPa whilst the nMOSFET gave about half the sensitivity at 2.40 mV/kPa. This was coupled with maximum power consumption of 0.19 mW and 0.39 mW for the pMOSFET and nMOSFET respectively. This shows a highly sensitive pressure sensor, with improved sensitivity on traditional piezoresistors as well as significantly higher sensitivity than current MOSFET based pressure sensors. Moreover, the maximum DC power consumption was only 190 µW and 390 µW for the pMOSFET and nMOSFET, respectively. This novel low-cost, low-power, high-sensitivity CMOS MEMS technology with on-chip electronics could be used towards the implementation of MOSFET based pressure transduction in a multitude of industrial and other applications.

Towards an Ultra-Sensitive Temperature Sensor for Uncooled Infrared Sensing in CMOS⁻MEMS Technology.

Microbolometers and photon detectors are two main technologies to address the needs in Infrared Sensing applications. While the microbolometers in both complementary metal-oxide semiconductor (CMOS) and Micro-Electro-Mechanical Systems (MEMS) technology offer many advantages over photon detectors, they still suffer from nonlinearity and relatively low temperature sensitivity. This paper not only offers a reliable solution to solve the nonlinearity problem but also demonstrate a noticeable potential to build ultra-sensitive CMOS–MEMS temperature sensor for infrared (IR) sensing applications. The possibility of a 31× improvement in the total absolute frequency shift with respect to ambient temperature change is verified via both COMSOL (multiphysics solver) and theory. Nonlinearity problem is resolved by an operating temperature sensor around the beam bending point. The effect of both pull-in force and dimensional change is analyzed in depth, and a drastic increase in performance is achieved when the applied pull-in force between adjacent beams is kept as small as possible. The optimum structure is derived with a length of 57 µm and a thickness of 1 µm while avoiding critical temperature and, consequently, device failure. Moreover, a good match between theory and COMSOL is demonstrated, and this can be used as a guidance to build state-of-the-art designs.

Piezoresistive temperature sensors fabricated by a surface micromachining CMOS MEMS process

This paper presents a micromachined monocrystalline silicon piezoresistive temperature sensor fabricated by a surface micromachining CMOS (Complementary Metal Oxide Semiconductor) MEMS (Micro-Electro-Mechanical System) process. The design of the temperature sensor is based on the structure of the multi-layer cantilever beam and the bimetallic effect. The temperature change of the cantilever beam is translated into the change of the piezoresistance’s value. The test results show that the sensitivities of the sensors are 27.9 mV/°C with 100 Ω/▯ piezoresistance between −40 °C to 60 °C and 7.4 mV/°C with 400 Ω/▯ piezoresistance between −90 °C to 60 °C. The temperature sensor proposed in this paper can be used in radiosondes for its low operating temperature (as low as −90 °C), small size (below 1 mm2) and low heat capacity.

Experiments on MEMS Integration in 0.25 μm CMOS Process.

In this paper, we share our practical experience gained during the development of CMOS-MEMS (Complementary Metal-Oxide Semiconductor Micro Electro Mechanical Systems) devices in IHP SG25 technology. The experimental prototyping process is illustrated with examples of three CMOS-MEMS chips and starts from rough process exploration and characterization, followed by the definition of the useful MEMS design space to finally reach CMOS-MEMS devices with inertial mass up to 4.3 g and resonance frequency down to 4.35 kHz. Furthermore, the presented design techniques help to avoid several structural and reliability issues such as layer delamination, device stiction, passivation fracture or device cracking due to stress.

CMOS MEMS Hot-Film Thermoelectronic Flow Sensor

In this article, we present a complementary metal-oxide semiconductor microelectromechanical system (CMOS MEMS) thermoelectronic flow sensor and discuss the advantages of employing anemometric and calorimetric transduction principles simultaneously. This readout concept exploits the fact that anemometric flow sensors take advantage of the maximum temperature generated within the device and, thus, are provided with the maximum flow sensitivity, while calorimetric flow sensors have the temperature sensing elements placed away from this maximum temperature region and, thus, are intrinsically less sensitive. At the same time, fluid flow direction discrimination in bidirectional flow sensors can be achieved by simply looking at the polarity of the differential signal coming from the temperature sensors placed aside the heating element. We also show that thermoelectronic flow sensors can benefit by having temperature sensors formed by an array of diodes to further enhance the device sensitivity. Although we apply these concepts to a sensor with a nonoptimum design and lacking any support electronics (e.g., filters, amplifiers, constant temperature driving circuitry, etc.), results are among the best ever reported in literature (including non-CMOS technologies), thus showing the high potential of our technology.

CMOS-MEMS Micro-Mirror Arrays by Post-Processing ASMC 0.35- $\mu \text{m}$ CMOS Chips

An electrostatic bi-stable $4\times 4$ micro-mirror array is implemented by using the standard Advanced Semiconductor Manufacturing Corporation 0.35- $\mu \text{m}$ 2-Poly-3-Metal fabless complementary metal-oxide-semiconductor microelectromechanical systems (CMOS-MEMS) process. Mechanical structures, including mirrors $(18 ~\mu \text {m} \times 18 ~\mu \text{m}$ in area each), electrostatic actuation mechanisms, and the suspensions, are made in the top three metal layers. Typical static pull-in voltage is tested to be 49 V and the maximum tilt angle is estimated to be 14.6°. The micro mirror can be operated at frequencies upward of 11 kHz at least. Total lifetime of more than 134.5 h, $4.8\times 10^{9}$ cycles, is tested. To avoid stiction during the process, the micro-mirror array is sacrificial-released from the substrate after the CMOS process by using reactive ion etching (RIE) and photoresist-assisted wet etching. Micro-mirror-wise processing yield of 99.3% after the release implies the robustness of the developed CMOS-MEMS process. [2017-0180]

Curvature of BEOL Cantilevers in CMOS-MEMS Processes

This paper presents the curvature characterization results of released back-end-of-line $5~\mu \text{m}$ -wide cantilevers for two different 0.18- $\mu \text{m}$ 1P6M complementary metal–oxide semiconductor microelectromechanical systems processes. Results from different runs and lots from each foundry are presented. The methodology and accuracy of the characterization approach, based on optical measurements of test cantilever curvature, are also discussed. Special emphasis is given to the curvature average and variability as a function of the number of stacked layers. Analythical equations for modeling the bending behavior of stacked cantilevers as a function of the tungsten (W) vias that join the metal layers are presented. In addition, the effect of various post-processing conditions and design techniques on the curvature of both single and stacked cantilevers is analyzed. In particular, surpassing certain time-dependent temperature stress conditions after release lead to curvature shifts larger than one order of magnitude. Also, the W via design was found to strongly affect the curvature of the test cantilevers. [2016-0293]