AZ4620 Photoresist as an Alternative Sacrificial Layer for Surface Micromachining
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https://doi.org/10.1007/s11664-020-08438-7 Ó 2020 The Minerals, Metals & Materials Society
AZ4620 Photoresist as an Alternative Sacrificial Layer for Surface Micromachining ASHUDEEP MINHAS,1,2 ANUROOP BAJPAI,1 KHUSHBU MEHTA,1 PREM KUMAR,1 AMIT KUMAR,1 and DEEPAK BANSAL1,3 1.—CSIR-Central Electronics Engineering Research Institute (CEERI), Pilani 333031, India. 2.—e-mail: [email protected]. 3.—e-mail: [email protected]
The mechanical actuation of suspended structures in microelectromechanical system (MEMS) switches plays an important role in obtaining an open or short circuit in radio-frequency (RF) transmission lines. These micromachined switches have moving parts which are realized by a sacrificial layer. Several sacrificial materials have been utilized in the fabrication of MEMS structures. The traditional method of using metal such as copper or nickel as a sacrificial layer is difficult due to metal etchant compatibility issues. A photoresist is the best choice for this process. Generally, the HiPR photoresist has been found to be suitable for the role of sacrificial layer. However, the HiPR is no longer available in the commercial market. As an alternative to the HiPR, the AZ4620 photoresist can be used. In this paper, a unit process optimization technique is described featuring an AZ4620 photoresist as a sacrificial layer for the microfabrication of a suspended structure. The AZ4620 meets all the requirements for the development of RF MEMS switches. Hence, the recipe and fabrication technique are optimized according to the required thickness. Preliminary measurements of the fabricated switch beam indicate that the required gap has been achieved. This optimized process is compatible with standard MEMS technology. Key words: RF MEMS switches, sacrificial layer, photoresist, AZ4620
INTRODUCTION Over the past two decades, amazing advances in microelectromechanical system (MEMS) technology have enabled the design and fabrication of micromechanical radio-frequency (RF) switches. These types of MEMS switches have been utilized in radiofrequency-wave to millimeter-wave circuit design and are best suited for applications in a frequency range of 0.1–110 GHz.1,2 RF MEMS switches have compact size, high Q-factor, high isolation, lower power consumption and low insertion loss, and handle much more power compared with semiconductor switches. These remarkable features of RF
(Received June 23, 2020; accepted August 20, 2020)
MEMS switches make them attractive for use in defense, radar, satellite, space and 5G communication systems.1–4 Radio-frequency MEMS switching devices are developed by microfabrication technology, where the mechanical actuation of a suspended structure results in an ON and OFF state of a switch.5 The two basic categories of RF MEMS switches are ohmic4,6 and capacitive.7,8 In both the cases, a micromachined switch is operated by the mechanical displacement of suspended beams or membranes. Generally, a RF MEMS switch comprises a switching actuator, transmission line, contacts and support eleme
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