Unoxidized porous Si as an isolation material for mixed-signal integrated circuit applications

Abstract

Articles you may be interested inMonolithic integration of common mode filters with electrostatic discharge protection on silicon/porous silicon hybrid substrate Appl. Phys. Lett.An isolation technology for radio frequency ͑rf͒ applications based on unoxidized porous Si ͑PS͒ is demonstrated. This study examines all the important issues pertinent to incorporating PS with Si very-large-scale integration ͑VLSI͒ technology, where PS is used as a semi-insulating material. Specifically, the issues on rf isolation performance of PS as a function of porosity ͓from coplanar waveguide ͑CPW͒ line measurements͔ and PS thickness ͑from on-chip inductors͒ and the stress generated from incorporating PS regions by anodization are discussed in detail. CPW line measurements show that the relative dielectric constant of PS films decreases from 9 to 3 with increasing porosity from 24% to 78%. PS is a very low loss material with loss tangent Ͻ0.001 at 20 GHz when its porosity is above 51%. rf crosstalk through a Si substrate can be reduced to that through air by inserting a PS trench between noise generating circuit and noise sensing circuit. On-chip spiral inductors fabricated on top of PS regions of through-the-wafer thickness have Q max of about 29 at 7 GHz and resonant frequency higher than 20 GHz. With the additional advantage of planar topography and mechanical integrity, we show that unoxidized PS is an outstanding material for rf isolation in Si VLSI.

Fabrication techniques and RF performances of transmission lines on polymer substrates

“…Using quartz and high-resistivity silicon as substrates has been investigated, however the material costs are high. Adopting a layer of silicon dioxide [1], silicon nitride or oxidized porous silicon as an isolation layer may present a problem of thermal expansion mismatching between the silicon substrate and these dielectric layers [2]. Using the unoxidized porous silicon as a dielectric layer avoids the problem of thermal expansion mismatching [2], yet it limits many RF MEMS applications and is not suited to flexible processes due to the usage of hydrofluoric acid during the process of forming unoxidized porous silicon.…”

Geometry-dependent band shift and dielectric modification of nanoporous Si nanowires

“…Therefore, the modulation of electronic and optoelectronic properties of np-Si has attract intense research interest due to their widely application in nanoscale physics and silicon-based devices 2 – 5 . For example, compared with silicon-based insulators, np-Si as substrate isolation material in Si-integrated RF devices shows a lot of significant advantages 6 – 9 , including elimination of RC signal delay, reduction of the power consumption and wire cross talk. These advantages are realized as a result of that controlled porosity could reduce the effective permittivity.…”

Dielectric properties of porous silicon for use as a substrate for the on-chip integration of millimeter-wave devices in the frequency range 140 to 210 GHz

“…Such a substrate is a thick porous Si layer with high porosity, which can be optimized for best device performance by choosing the appropriate layer thickness, in order to minimize electromagnetic propagation losses into Si, and the appropriate low values of the dielectric permittivity, ε r , and loss tangent. These last values are tunable by changing the material structure and morphology [ 1 - 6 ].…”