RF MEMS Shunt Capacitive Switches Using AlN Compared to $\hbox{Si}_{3}\hbox{N}_{4}$ Dielectric

Abstract

RF microelectromechanical systems (MEMS) capacitive switches for two different dielectrics, aluminum nitride (AlN) and silicon nitride <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$(\hbox{Si}_{3}\hbox{N}_{4})$</tex></formula> , are presented. The switches have been characterized and compared in terms of DC and RF performance (5–40 GHz). Switches based on AlN have higher down-state capacitance for similar dielectric thicknesses and provide better isolation and smaller insertion losses compared to <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\hbox{Si}_{3}\hbox{N}_{4}$ </tex></formula> switches. Experiments were carried out on RF MEMS switches with stiffening bars to prevent membrane deformation due to residual stress and with different spring and meander-type anchor designs. For a <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\sim$</tex></formula> 300-nm dielectric thickness, an air gap of 2.3 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\mu\hbox{m}$</tex></formula> and identical spring-type designs, the AlN switches systematically show an improvement in the isolation by more than <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$-$</tex> </formula> 12 dB ( <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$-$</tex></formula> 35.8 dB versus <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$-$</tex></formula> 23.7 dB) and a better insertion loss ( <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$-$</tex></formula> 0.68 dB versus <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$-$</tex></formula> 0.90 dB) at 40 GHz compared to <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\hbox{Si}_{3}\hbox{N}_{4}$</tex></formula> . DC measurements show small leakage current densities for both dielectrics ( <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$&lt;10^{-8}\ \hbox{A/cm}^{2}$</tex> </formula> at 1 MV/cm). However, the resulting leakage current for AlN devices is ten times higher than for <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\hbox{Si}_{3}\hbox{N}_{4}$</tex></formula> when applying a larger electric field. The fabricated switches were also stressed by applying different voltages in air and vacuum, and dielectric charging effects were investigated. AlN switches eliminate the residual or injected charge faster than the <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\hbox{Si}_{3}\hbox{N}_{4}$</tex></formula> devices do. <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\hfill$</tex></formula> [2011-0359]