Wafer-scale platform for on-chip 3D radio frequency lumped passive components using metal self-rolled-up membrane technique

A wafer-scale metal self-rolled-up membrane platform has been proposed for the design and fabrication of radio-frequency on-chip lumped passive components, which is demonstrated on a commercial 4-inch sapphire batch fabrication line. Compared to the traditional methodology including planar or SiN_x based self-rolled-up membrane processing technologies to obtain the most basic passive lumped components, such as inductors and capacitors on the chip, this platform enables more compact three-dimensional construction of the component device structure with higher electrical performance. For demonstration, batches of wafer-scale RF inductors and capacitors are fabricated through precise design based on electromagnetic analysis. Measurement results show that radio-frequency inductor samples obtain inductance of 0.6 nH~3.4 nH and a maximum quality factor of 3.1 ~ 7.3 with the largest inductance density of 2.26 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mspace></mml:mspace> <mml:mi>μ</mml:mi> <mml:mi>H</mml:mi> <mml:mo>/</mml:mo> <mml:msup><mml:mrow><mml:mi>mm</mml:mi></mml:mrow> <mml:mrow><mml:mn>2</mml:mn></mml:mrow> </mml:msup> </mml:math> , and a typical RF capacitor sample show capacitance of 0.5 pF with the largest capacitance density of 1528.4 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>pF</mml:mi> <mml:mo>/</mml:mo> <mml:msup><mml:mrow><mml:mi>mm</mml:mi></mml:mrow> <mml:mrow><mml:mn>2</mml:mn></mml:mrow> </mml:msup> </mml:math> . After post electroplating, coper layer thickness of a 1.1 nH inductor is increased to be ~ 2.7 μm from 120 nm with the inner diameter of 80 μm, and the maximum quality factor is significantly increased to 18 @ 1.4 GHz. Standalone inductors can be successfully cut off from a 4-inch sapphire wafer by using laser modification cutting.