Thick-membrane-operated radio frequency switches with wafer-level package using gold compressive bonding

Abstract

An electrostatically actuated radio frequency (rf) switch is fabricated using a thick silicon membrane, and the device is packaged using a high resistivity silicon cap wafer with a gold (Au) thermocompressive bonding method. To achieve an rf switch that can operate at low voltage, a thick membrane with a pivot under the membrane is used. This design makes it possible to maintain the very small gap between the electrodes and the membrane without bending. A cavity with a pivot-patterned silicon wafer and a coplanar waveguide (CPW) signal-line-formed glass wafer is bonded using an anodic bonding method. After a mechanical polishing process, a deep reactive ion etcher is used to fabricate the membrane structure with a spring and a spring bar. To package the fabricated rf switch, an Au thermocompressive bonding process is used. A 1-µm-thick sputtered Au layer is used as intermediate bonding material. The bonding temperature and pressure are 350 °C and 63 MPa, respectively, and the time duration of the bonding is set to 30 min. The electrodes of the switch and the electrical contact pads on the cap wafers are interconnected via a hole and a sputtered Au metal layer. The total size of the complete packaged rf switch is 2.2 × 1.85 mm, and its rf characteristics have been measured using a Hewlett−Packard (HP) 8510C network analyzer. The measured driving voltage is approximately 16 V, the isolation is approximately −38.4 dB, and the insertion loss is approximately −0.43 dB at 2 GHz.