Sputtered Encapsulation as Wafer Level Packaging for Isolatable MEMS Devices: A Technique Demonstrated on a Capacitive Accelerometer (original) (raw)
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Single wafer encapsulation of MEMS devices
IEEE Transactions on Advanced Packaging, 2003
Packaging of micro-electro-mechanical systems (MEMS) devices has proven to be costly and complex, and it has been a significant barrier to the commercialization of MEMS. We present a packaging solution applicable to several common MEMS devices, such as inertial sensors and micromechanical resonators. It involves deposition of a 20 μm layer of epi-polysilicon over unreleased devices to act as a
Wafer-level thin-film encapsulation for MEMS
Microelectronic Engineering, 2009
The diversity and complexity of many microelectromechanical systems (MEMS), combined with the mechanical nature of the devices involved, means that the handling, dicing and packaging of these structures can pose many problems. So-called 'zero-level' packaging options are now often used to protect the devices at the wafer scale before the wafer is diced and sent for conventional packaging. This paper describes a novel process flow for the fabrication of integrated MEMS thin-film packages within a lowtemperature, CMOS-compatible process. A double sacrificial layer is used, which encapsulates the device of interest within a shell of silicon oxide. The sacrificial layer is then removed through lateral etch channels and the shell is sealed. The technique requires minimal extra wafer space, allows the use of low-temperature materials within the process flow, and the novel channel design means that the shell may be easily sealed. Preliminary visual and electromechanical tests using simple fixed-fixed beam test structures indicate that the package is sealed, the device is undamaged and that encapsulation has little or no effect on device performance.
Cost-Efficient Wafer-Level Capping for MEMS and Imaging Sensors by Adhesive Wafer Bonding
Micromachines, 2016
Device encapsulation and packaging often constitutes a substantial part of the fabrication cost of micro electro-mechanical systems (MEMS) transducers and imaging sensor devices. In this paper, we propose a simple and cost-effective wafer-level capping method that utilizes a limited number of highly standardized process steps as well as low-cost materials. The proposed capping process is based on low-temperature adhesive wafer bonding, which ensures full complementary metal-oxide-semiconductor (CMOS) compatibility. All necessary fabrication steps for the wafer bonding, such as cavity formation and deposition of the adhesive, are performed on the capping substrate. The polymer adhesive is deposited by spray-coating on the capping wafer containing the cavities. Thus, no lithographic patterning of the polymer adhesive is needed, and material waste is minimized. Furthermore, this process does not require any additional fabrication steps on the device wafer, which lowers the process complexity and fabrication costs. We demonstrate the proposed capping method by packaging two different MEMS devices. The two MEMS devices include a vibration sensor and an acceleration switch, which employ two different electrical interconnection schemes. The experimental results show wafer-level capping with excellent bond quality due to the re-flow behavior of the polymer adhesive. No impediment to the functionality of the MEMS devices was observed, which indicates that the encapsulation does not introduce significant tensile nor compressive stresses. Thus, we present a highly versatile, robust, and cost-efficient capping method for components such as MEMS and imaging sensors.
Chemically resistant encapsulant to enable a novel MEMS fabrication process
2013
We have proposed and demonstrated a novel sequence in MEMS fabrication process flow. The novel MEMS fabrication process flow can be shortly described as a “packaging first, MEMS release second”, whereas a standard process starts form MEMS release and ends up with packaging. The process is explored on a 3D capacitive MEMS sensor (3 × 3 mm2). Unreleased wafer is singulated by sawing on individual dies, then the individual sensor is mounted to the package, wire bonded and encapsulated. Because the sensors are still unreleased there is no damage occurred during the assembly. However the choice for the encapsulant material is not evident. The encapsulant must survive the chemical attack during the MEMS release process (mixture of 73%HF and IPA (isopropanol)), followed by a triple rinse in IPA. We pre-selected 6 different encapsulants: a silicone-, an epoxy- and an urethane-based. At least one encapsulant passed the acceptance criteria: there is no delamination, there is no texture change...
Poly-SiGe-Based MEMS Thin-Film Encapsulation
Journal of Microelectromechanical Systems, 2000
This paper presents an attractive poly-SiGe thin-film packaging and MEM (microelectromechanical) platform technology for the generic integration of various packaged MEM devices above standard CMOS. Hermetic packages with sizes up to 1 mm 2 and different sealed-in pressures (∼100 kPa and ∼2 kPa) are demonstrated. The use of a porous cover on top of the release holes avoids deposition inside the cavity during sealing, but leads to a sealed-in pressure of approximately 100 kPa, i.e. atmospheric pressure. Vacuum (∼2 kPa) sealing has been achieved by direct deposition of a sealing material on the SiGe capping layer. Packaged functional accelerometers sealed at around 100 kPa have an equivalent performance in measuring accelerations of about 1 g compared to a piezoelectric commercial reference device. Vacuum-sealed beam resonators survive a 1000 h 85 • C/85%RH highly accelerated storage test and 1000 thermal cycles between −40 • C and 150 • C.
An SOI–MEMS technology using substrate layer and bonded glass as wafer-level package
Sensors and Actuators A: Physical, 2002
We have developed a novel (silicon-on-insulator (SOI), microelectromechanical systems (MEMS)) SOI±MEMS technology combined with anodic bonding process. A metal layer on the glass substrate can provide out-of-plane electrodes and interconnects. More importantly, a wafer-level package of mechanical structures constructed by the top layer of the SOI wafer can be formed by the glass substrate and the substrate layer of the SOI wafer simultaneously. The package can protect fragile mechanical structures during post-release processes, such as dicing, mounting and wire bonding as an ordinary IC wafer. In addition, the wafer-level package can directly provide a specialized package, such as a vacuum package for gyroscopes. No special process other than micromachining is needed. #
Sensors and Actuators A-physical, 2007
In this paper, we present a novel technique for encapsulation of MEMS devices. The technique is demonstrated to address two issues related to the use of in-plane thermal actuators for BioMEMS applications. First, an encapsulation process is described to provide protection to a MEMS actuator from debris and other particulate matter when deployed in a biological environment. The encapsulation structure consists of a multilayer wall around the actuator and a surface micromachined polysilicon cap. A small clearance is provided around a piston that transmits motion from the actuator to the external world. In air, the packaged actuator performance is comparable to that of an unpackaged actuator, thus indicating successful encapsulation without any damage to the actuator. Second, this packaging approach is used to address the issue of reduction in efficiency of the thermal actuator in liquids by coating the packaged actuator with a thin conformal hydrophobic layer. This prevents liquid from entering the encapsulation, thus isolating the hot actuator components from the liquid. Experimental results show that efficiency of the packaged actuator in water improved giving a performance similar to that observed in air, suggesting an isolation of the hot actuator components from the liquid. Although the technique is demonstrated for thermal actuators, it is also applicable to other MEMS devices and in-plane actuators such as electrostatic comb drives for engineering as well as biological applications.
Low-temperature thin film encapsulation for MEMS with silicon nitride/chromium cap
IEEE Sensors Journal, 2023
In this work, a low-temperature fabrication process of thin film encapsulation (TFE) with silicon nitride/chromium cap is proposed for large-size (750 µm x 300 µm) packaging of microelectromechanical systems (MEMS). A FEM model was developed to evaluate the shape of TFE as a function of the residual stress and the thickness of the sealing layer, providing useful guidelines for the fabrication process. The low temperature of 200 °C, which was used in the plasma-enhanced chemical vapor deposition of the silicon nitride capping layer, allowed an organic sacrificial material to be employed for the definition of the encapsulation area. Silicon nitride/chromium (1 µm/20 nm) bilayer was demonstrated to be successful to overcome the technological limitations that affect the creation of cap holes with size of ~2 µm on high topography substrates, as in the case of MEMS. Plasma focused ion beam (PFIB) and scanning electron microscopy (SEM) techniques were used in combination to gain deeper insight into the sealing process of cap holes. Specifically, a PFIB-SEM serial section procedure was developed, resulting to be a powerful tool to directly observe the sealing profile above cap holes. Hence, the presented results greatly contribute to overcome the main technological/reliability issues of TFE, paving the way for the widespread application of the proposed encapsulation methodology to the most used MEMS devices, as radio-frequency (RF) switches, transducers, actuators, sensors and resonators.
Packaging and Non-Hermetic Encapsulation Technology for Flip Chip on Implantable MEMS Devices
Journal of Microelectromechanical Systems, 2012
We report here a successful demonstration of a flip-chip packaging approach for a microelectromechanical systems (MEMS) device with in-plane movable microelectrodes implanted in a rodent brain. The flip-chip processes were carried out using a custom-made apparatus that was capable of the following: 1) creating Ag epoxy microbumps for first-level interconnect; 2) aligning the die and the glass substrate; and 3) creating non-hermetic encapsulation (NHE). The completed flip-chip package had an assembled weight of only 0.5 g significantly less than the previously designed wire-bonded package of 4.5 g. The resistance of the Ag bumps was found to be negligible. The MEMS micro-electrodes were successfully tested for its mechanical movement with microactuators generating forces of 450 μN with a displacement resolution of 8.8 μm/step. An NHE on the front edge of the package was created by patterns of
Very Thin Packaging of Capped MEMS Accelerometer Device
2005 7th Electronic Packaging Technology Conference
Analog Devices Inc. (ADI) has been a major supplier of accelerometer devices in hermetic packages used for crash detection and vehicle dynamic control in the automotive industry. A major market pull from the handheld customers makes it imperative to develop thin plastic packaging solution for MEMS accelerometer. This paper details the backgrinding process developed to successfully thin the wafer-level-capped MEMS