Millimeter-wave MEMS capacitive switch in vacuum-sealed in-line wafer level package

In this paper, we present a millimeter-wave microelectromechanical systems (MEMS) switch with a microsecond switching time. The optimization of the mechanical structure, application of high actuation voltages and encapsulation with a vacuum-sealed package result in a higher speed with which a beam of the MEMS switch is pulled in and pulled out. In order to reduce the packaging cost, we encapsulate the MEMS switch using an in-line wafer level package (WLP) which is built during the same complementary metal-oxide semiconductor (CMOS) process in which the MEMS switch is built. The fabricated MEMS switch is a shunt circuit and capacitive contact type. The dimensions of the in-line WLP are 500 ¿m wide by 500 ¿m long. The measurement results show an insertion loss of 0.5 dB and an isolation of 15 dB at a frequency of 50 GHz. The measured switching time is 2.0 ¿s or less. This is the shortest switching time of a MEMS capacitive switch for millimeter wave applications as far as the authors know.

I. Introduction

Microelectromechanical systems (MEMS) switches exhibit better insertion loss, linearity and power consumption than semiconductor switches in a high-frequency band [1]. Hence, we expect to utilize them in millimeter wave applications such as phased array radar and wireless communication systems. Such applications require that the time for switching diversity antennas and the time for switching transmitting/receiving circuits be short. To realize the short switching time, MEMS switches must have an electrostatic actuation mechanism, be actuated by high voltages and consist of a small beam with a high spring constant [2]. However, the shunt capacitive switch requires a large beam for obtaining a high isolation performance. Hence, we cannot optimize the size of the beam for only the purpose of shortening pull-in and pull-out times.