Lifetime Extension of RF MEMS Direct Contact Switches in Hot Switching Operations by Ball Grid Array Dimple Design (original) (raw)
Related papers
2010
The implementation of direct contact RF MEMS switches is challenging owing to their unstable contact resistance and low power handling/delivery. This paper carefully studies RF MEMS switch contact behavior and proposes a new method to suppress its instability leading to device failure. Our study supports the hypothesis that MEMS contact switches fail primarily due to contact necking. Using the proposed method, we demonstrate the ability to keep MEMS switch contact resistance under ~0.05 ! in high-cycle cold-switching while a high contact current of >0.9 A is handled/delivered. 978-1-4244-5763-2/10/$26.00 ©2010 IEEE
Metal contact reliability of RF MEMS switches
Proc. SPIE, 2007
It is well-recognized that MEMS switches, compared to their more traditional solid state counterparts, have several important advantages for wireless communications. These include superior linearity, low insertion loss and high isolation. Indeed, many potential ...
Force dependence of RF MEMS switch contact heating
2004
Contact-type RF MEMS switches have demonstrated low onstate resistmce, high off-state impedance, and very large bandwidth; however, their power handling capability is low due to failure caused by contact heating. This paper examines contact heating by measuring V-I curves for contacts in gold switches. Multiphysics modeling allows extraction of contact temperature. Contacts are found to soften and self-anneal at a temperature of about IOOT, corresponding to a contact voltage of about 80 mV. Larger contact force induces a larger decrease in contact resistance during softening, suppressing contact heating. The data provide a better understanding of micro-scale contact physics, leading to design for switches for improved power-handling capability.
Temperature dependence of asperity contact and contact resistance in gold RF MEMS switches
Journal of Micromechanics and Microengineering, 2009
Experimental measurements and modeling predictions were obtained to characterize the electro-mechanical response of two different gold contact radio frequency microelectromechanical system (RF MEMS) switches due to variations in the temperature and applied contact voltage. A three-dimensional surface roughness profile from AFM measurements of the top contact surface of a sample RF MEMS switch was used to obtain modeling predictions of the time-dependent deformation of the asperity microcontacts, real areas of contact, number of asperity microcontacts and constriction resistance. The experimental data indicated a decrease in the overall resistance and a decrease in the creep mechanism at 77 K and 5.6 K when compared to measurements at 293 K. At 293 K, there is more contact area per unit time, and the resistance drop from the increase in real contact area dominates the resistance increase due to asperity heating. At 77 K, the creep rate is reduced, and fewer asperities are in contact. At 5.6 K, the change in contact area over time is small, and the contact resistance measurement is dominated by the Joule heating. The data presented and constriction resistance modeling for gold RF MEMS switches show that temperature plays a significant role in the creep deformation and heating of switch contacts.
A packaged, high-lifetime ohmic MEMS RF switch
2003
An electrostatically actuated broadband ohmic microswitch has been developed that has applications from DC through the microwave region. The microswitch is a 3terminal device based on a cantilever beam and is fabricated using an all-metal, surface micromachining process. It operates in a hermetic environment obtained through a waferbonding process. Characteristics of the wafer-level packaged switch include DC on-resistance of less than 1 Ohm with an actuation voltage of 80 V, lifetime of greater than 10 10 cycles with on-resistance variation of less than 0.2 Ohm and current handling capability of 1 Ampere. Key RF characteristics at 2 GHz include an insertion loss of 0.32 dB and isolation of 33 dB for our 4-contact microswitch. Preliminary measurements at higher microwave frequencies are extremely promising with full characterization and planned product improvements underway.
Metal contact reliability of RF MEMS switches
Reliability, Packaging, Testing, and Characterization of MEMS/MOEMS VI, 2007
It is well-recognized that MEMS switches, compared to their more traditional solid state counterparts, have several important advantages for wireless communications. These include superior linearity, low insertion loss and high isolation. Indeed, many potential applications have been investigated such as Tx/Rx antenna switching, frequency band selection, tunable matching networks for PA and antenna, tunable filters, and antenna reconfiguration. However, none of these applications have been materialized in high volume products to a large extent because of reliability concerns, particularly those related to the metal contacts. The subject of the metal contact in a switch was studied extensively in the history of developing miniaturized switches, such as the reed switches for telecommunication applications. While such studies are highly relevant, they do not address the issues encountered in the sub 100µN, low contact force regime in which most MEMS switches operate. At such low forces, the contact resistance is extremely sensitive to even a trace amount of contamination on the contact surfaces. Significant work was done to develop wafer cleaning processes and storage techniques for maintaining the cleanliness. To preserve contact cleanliness over the switch service lifetime, several hermetic packaging technologies were developed and their effectiveness in protecting the contacts from contamination was examined. The contact reliability is also very much influenced by the contact metal selection. When pure Au, a relatively soft metal, was used as the contact material, significant stiction problems occurred when clean switches were cycled in an N 2 environment. In addition, various mechanical damages occurred after extended switching cycling tests. Harder metals, while more resistant to deformation and stiction, are more sensitive to chemical reactions, particularly oxidation. They also lead to higher contact resistance because of their lower electrical conductivity and smaller real contact areas at a given contact force. Contact reliability issues could also be tackled by improving mechanical designs. A novel collapsing switch capable of generating large contact forces (>300µN) was shown to be less vulnerable to contamination and stiction.
Reliability Study of Low-Voltage RF MEMS Switches
2002
The reliability and performance of a low-voltage metal-tometal contact shunt RF MEMS switch is investigated. The switch featured is compatible with standard MMIC processing steps. The best rf performance shows insertion loss of less that 0.1 dB and isolation of greater than 22 dB for all frequencies up to 40 GHz. Switching times are less than 25 µs. Lifetimes of 3×10 8 cycles have been achieved for tests with no input signal, and 1.3×10 6 cycles for tests with continuous input. The failure mechanism is degradation of the metal-to-metal contact, and stiction problems have been avoided through careful processing and testing conditions.
Fabrication of high power RF MEMS switches
Microelectronic Engineering, 2006
High power RF MEMS switches have been designed and fabricated. The switches are composed of a matrix of ohmic contact cantilevers and bridges. Optimized fabrication processes have been developed to improve planarization on contact surface and reduce residual stress in switch beams, which ensure a reasonable flat and smooth cantilever and membrane bridge for operation at high RF power and low actuation voltage.
Surface roughness, asperity contact and gold RF MEMS switch behavior
Journal of Micromechanics and Microengineering, 2007
Modeling predictions and experimental measurements were obtained to characterize the electro-mechanical response of radio frequency (RF) microelectromechanical (MEM) switches due to variations in surface roughness and finite asperity deformations. Three-dimensional surface roughness profiles were generated, based on a Weierstrass-Mandelbrot fractal representation, to match the measured roughness characteristics of contact bumps of manufactured RF MEMS switches. Contact asperity deformations due to applied contact pressures were then obtained by a creep constitutive formulation. The contact pressure is derived from the interrelated effects of roughness characteristics, material hardening and softening, temperature increases due to Joule heating and contact forces. This modeling framework was used to understand how contact resistance evolves due to changes in the real contact area, the number of asperities in contact, and the temperature and resistivity profiles at the contact points. The numerical predictions were qualitatively consistent with the experimental measurements and observations of how contact resistance evolves as a function of deformation time history. This study provides a framework that is based on integrated modeling and experimental measurements, which can be used in the design of reliable RF MEMS devices with extended life cycles.