Intrinsic Stress in Porous Silicon Layers Formed by Anodization in HF Solution

Unagami, Takashi

doi:10.1149/1.1837686

Cited by 30 publications

(22 citation statements)

References 3 publications

(2 reference statements)

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“…The mechanical instability of porous Si is directly related to the strain that is induced in the film as it is produced in the electro-chemical etching process [74], and the volume expansion that accompanies thermal oxidation can also introduce strain. Mild chemical oxidants presumably attack porous Si preferentially at Si-Si bonds that are the most strained, and hence most reactive [16].…”

Section: Oxidation Of Porous Simentioning

confidence: 99%

Porous silicon in drug delivery devices and materials☆

Anglin

Cheng

Freeman

et al. 2008

Advanced Drug Delivery Reviews

801

618

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Porous Si exhibits a number of properties that make it an attractive material for controlled drug delivery applications: The electrochemical synthesis allows construction of tailored pore sizes and volumes that are controllable from the scale of microns to nanometers; a number of convenient chemistries exist for the modification of porous Si surfaces that can be used to control the amount, identity, and in vivo release rate of drug payloads and the resorption rate of the porous host matrix; the material can be used as a template for organic and biopolymers, to prepare composites with a designed nanostructure; and finally, the optical properties of photonic structures prepared from this material provide a self-reporting feature that can be monitored in vivo. This paper reviews the preparation, chemistry, and properties of electrochemically prepared porous Si or SiO 2 hosts relevant to drug delivery applications.

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Section: Oxidation Of Porous Simentioning

confidence: 99%

Porous silicon in drug delivery devices and materials☆

Anglin

Cheng

Freeman

et al. 2008

Advanced Drug Delivery Reviews

801

618

View full text Add to dashboard Cite

show abstract

“…The use of a surfactant is also thought to facilitate corrosion by helping to remove hydrogen bubbles generated during the anodic reaction. Use of ultrasonic agitation to remove H gas bubbles is also noted in the literature [32].…”

mentioning

confidence: 94%

Mechanical Effects of Galvanic Corrosion on Structural Polysilicon

Miller

Hughes

Wang

et al. 2007

J. Microelectromech. Syst.

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Abstract-The mechanical properties of miniaturized materials depend strongly on their structure, which can be altered by wet chemistry methods common in microsystems postprocessing. In a comprehensive and systematic study, we examine the dissolution of silicon when immersed in various hydrofluoric acid (HF)-based chemistries. Specifically, the frequency of mechanical resonance f R of microcantilever beams is used as a vehicle to examine the corrosion of polycrystalline silicon (polySi). A decrease in f R that occurs as a function of immersion time in HF was measured for microcantilevers as well as "comb drives" in contact with a noble metal (gold). Time-dependent variation was also observed in the modulus and hardness measured during indentation testing, sometimes with pronounced difference for specimens contacted to gold. Secondary sources of influence, such as in-plane-oriented residual strain (which remained unchanged), through-thickness-oriented residual strain gradient (increased away from the substrate), and electrical resistance (greatly increased) are examined, but were found not to significantly contribute to the decrease in fR of the microcantilevers. Morphological characterization identified attack on the surface along with grain delineation for the polySi, with the formation of a nanoscale porous layer at the near surface. The damage to the microcantilevers can be modeled by approximating the beams as a laminated composite structure. Such analysis suggests that damage, induced as the result of galvanic corrosion, results from the decreased stiffness of the near surface porous silicon (PS) layer as well as a change in the effective thickness of the beams. Last, corrosion damage is compared between eight representative HF-based chemistries. The measurements here suggest that the fabrication and postprocessing of microsystems components are important, because they can greatly influence the material properties, design, performance, lifetime, tribology, manufacture, and required operating environment of microscale and nanoscale devices.[

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“…Previous PS film stress studies focused on either in situ ultrahigh vacuum (UHV) [5] or treatment in N 2 below 350 ˚C [6,7], and thus did not investigate how PS stress evolves at temperatures higher than 475 ˚C [8] due to continued hydrogen desorption without ultrahigh vacuum conditions. Though the temperature dependence of PS stress and its relationship with hydrogen desorption have been reported [9,10], changes in stress after relatively high temperature annealing in N 2 or after repeated HF exposure, as would be common in a multistep PS-MEMS fabrication process, have not been investigated.…”

Section: Introductionmentioning

confidence: 99%