Single wafer encapsulation of MEMS devices (original) (raw)
Related papers
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.
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.
Sensors, 2008
This paper discusses sputtered silicon encapsulation as a wafer level packaging approach for isolatable MEMS devices. Devices such as accelerometers, RF switches, inductors, and filters that do not require interaction with the surroundings to function, could thus be fully encapsulated at the wafer level after fabrication. A MEMSTech 50g capacitive accelerometer was used to demonstrate a sputtered encapsulation technique. Encapsulation with a very uniform surface profile was achieved using spin-on glass (SOG) as a sacrificial layer, SU-8 as base layer, RF sputtered silicon as main structural layer, eutectic gold-silicon as seal layer, and liquid crystal polymer (LCP) as outer encapsulant layer. SEM inspection and capacitance test indicated that the movable elements were released after encapsulation. Nanoindentation test confirmed that the encapsulated device is sufficiently robust to withstand a transfer molding process. Thus, an encapsulation technique that is robust, CMOS compatible, and economical has been successfully developed for packaging isolatable MEMS devices at the wafer level.
Encapsulated micro mechanical sensors
Microsystem Technologies, 1994
Encapsulated micro mechanical sensors were fabricated using glass-silicon anodic bonding and an electrical feedthrough structure. Two parallel plates which can be used not only for capacitive sensors but also electrostatic actuators are adopted for integrated sensors as capacitive pressure sensors, accelerometers and resonating sensors. Micromachining technologies were developed for these packaged micro sensors. These include silicon etching technologies as laser assisted etching, deep RIE and in-process thickness monitoring during wet etching. Anodic bonding technologies which enable to incorporate a circuit inside the package and to keep a sealed cavity at a high vacuum are also developed.
An On-Chip Hermetic Packaging Technology for Micromechanical Devices
1998 Solid-State, Actuators, and Microsystems Workshop Technical Digest, 1998
A novel on-chip hermetic packaging technology utilizing electrostatic bonding and eutectic sealing is presented. Planarization of the lead transfers is not required since the leads conform to the interfacial layer by forming a eutectic seal with the bonding layer (amorphous polysilicon). The leads also have an isolation resistance of >4Gillsq. This approach requires only one masking step and exhibits low induced stress, high thermal shock resistance, and a leak rate of <10. 16 SCCM.
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.
MEMS Resonators: Getting the Packaging Right
Microelectromechanical Systems (MEMS) resonators have been investigated for over forty years but have never delivered the high performance and low cost required of commercial oscillators. Packaging technology has been one of the primary limitations. MEMS resonators must be enclosed in very clean environments because even small amounts of surface contamination can significantly change resonator frequency. In addition, since the packaging can dominate the product cost and the applications are often cost sensitive, the packaging should be inexpensive. These requirements have now been met by SiTime' s MEMS-First TM wafer-level encapsulation and packaging technology.
Challenges in the packaging of MEMS
Proceedings International Symposium on Advanced Packaging Materials. Processes, Properties and Interfaces (IEEE Cat. No.99TH8405)
The packaging of Micro-Electro-Mechanical Systems (MEMS) is a field of great importance to anyone using or manufacturing sensors, consumer products, or military applications. Currently much work has been done in the design and fabrication of MEMS devices but insufficient research and few publications have been completed on the packaging of these devices. This is despite the fact that packaging is a very large percentage of the total cost of MEMS devices. The main difference between IC packaging and MEMS packaging is that MEMS packaging is almost always application specific and greatly affected by its envirotient and packaging techniques such as die handling, die attach processes, and lid sealing. Many of these aspects are directly related to the materials used in the packaging processes. MEMS devices that are functional in wafer form can be rendered inoperable after packaging. MEMS dies must be handled only from the chip sides so features on the top surface are not damaged. This eliminates most current die pick-and-place fixtures. Die attach materials are key to MEMS packaging. Using hard die attach solders can create high stresses in the MEMS devices, which can affect their operation greatly. Lowstress epoxies can be high-outgassing, which can also affect device performance. Also, a low modulus die attach can allow the die to move during ultrasonic wirebonding resulting to low wirebond strength. Another source of residual stress is the lid sealing process. Most MEMS based sensors and devices require a hermetically sealed package. This can be done by pm~el seam welding the package lid, but at the cost of further induced stress on the die. Another issue of MEMS packaging is the media compatibility of the packaged device. MEMS unlike ICS often interface with their environment, which could be high pressure or corrosive. The main conclusion we can DISCLAIMER Portions of this document may be illegible in electronic image products. Images are produced from the best available original document. , , draw about MEMS packaging is that the package affects the performance and reliability of the MEMS devices. There is a gross lack of understanding between the package materials, induced stress, and the device performance. The material properties of these packaging materials are not well defined or understood. Modeling of these materials and processes is far from maturity. Current post-package yields are too low for commercial feasibility, and consumer operating environment reliability and compatibility are often difficult to simulate. With fu~her understanding of the materials properties and behavior of the packaging materials, MEMS applications can be fully realized and integrated into countless commercial and military applications.
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...