A lift-off process is used to pattern metals that are nonetchable. The success is dependent on the degree of undercutting of the bottom sacrificial layer and various methods were briefly discussed. It is shown that single-layer negative-tone 7µm thick MaN-1440 photoresist from Micro Resist Technology produces an excellent re-entrant profile for metal lift-off. The objectives for this paper will be to obtain a thickness of 7µm for MaN-1440 photoresist and to optimize and fine-tune the sidewall profile for effective lift-off. The results show that the undercut profile can be separately tuned by different photolithography parameters. It was found that the exposure energy determines the top CD while the bottom CD is determined solely by the developing time. The results showed exposure energy of 400mJ and a developing time of 200 seconds gave an ideal re-entrant profile. CDs ranging from 5µm to 250µm have been successfully patterned. Metal layers ranging from 0.11 to 5.8µm thick were lifted-off with no issues.
This paper presents design, fabrication, and characterization of a novel microelectromechanical microreed switch, which consists of two Ni 80 Fe 20 magnetic plates as microreeds. One is embedded in a silicon trench. The other is suspended above the substrate and supported by a pair of crab-leg flexures from the two sides. Both Ni 80 Fe 20 plates are split into two long, narrow strips to improve the sensitivity. The switch is actuated by bringing an external magnet closer to the switch. The magnetic field required to turn on the switch can be as low as 0.5 mT and the initial contact resistance is < 10 Ω with gold contacts. The switch has been tested to pass more than 40 million hot switching cycles at 2 mA current at room temperature when packaged at wafer level with SU-8 sealing. The die size is 1.7 × 1.8 × 1.1 mm 3 . The proposed microreed switch can be used as the proximity sensor to sense the magnetic field. It also has the potential to replace the conventional reed switch in portable electronics, such as cellular phones, hearing aids, and laptops, where conserving battery power and device size is critical.[
2011-0121]Index Terms-Magnetic switch, MEMS switch, nickel-iron alloy, reed.
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