Effect of radiation on silicon and borosilicate glass

A study was made that is logically divided into two parts, both involving radiation damage effects. The first is a study of the effects of neutron and gamma radiation on the dimensions of two borosilicate glasses, Pyrex® and Hova SD-2®. These two glasses are commonly used as substrates for silicon microelectromechanical (MEMS) devices, and radiation-induced compaction in a substra.te can have deleterious effects on device performance. Results are presented for density changes induced in both glasses by neutron irradiation. Pyrex was shown to compact at a rate of (in [delta]p[rho]/p[rho] per n/cm2̂) 8.14 x 10-̂20 (thermal) and 1.79 x 10-̂20 (fast). The corresponding results for Hoya SD-2 were 2.21 x 10-̂21 and 1.71 x 10-̂21, respectively. On a displacement per atom (dpa) basis, the compaction of the Pyrex was an order of magnitude greater than that of the Hoya SD-2. Our results are the first reported measurement of irridiation-induced densification in Hoya SD-2. The compaction of Pyrex agreed with a previous study. Our results for gamma irradiations were unexpected. Silicon MEMS strain gauges mounted on glass wafers were gamma-irradiated to hundreds of Mrad. Based on expectations from the literature, the Pyrex was supposed to compact to a level easily measurable by the MEMS strain gauges. Almost no substrate compaction registered in the strain gauges, however. It is hypothesized that the anodic bonding process (by which a silicon wafer was bonded to the glass before etching to create the MEMS strain gauges) was responsible for either 1) changing the bulk radiation response of the glass or 2) creating a layer near the bond interface which somehow prevented the MEMS strain gauges from registering the compaction that was occurring in the glass substrate. While not yet understood, this null result for apparent substrate compaction is of great importance to the problem of mechanically rad-hard MEMS, since it indicates that the response of an anodically bonded Si-glass system to radiation is not simply the sum of the effects on the unbonded materials. To investigate this further, glass samples were prepared in various stages of the anodic bonding process (which involves heating in the presence of an electric field), then irradiated with neutrons. No difference in bulk compaction was noted among the

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Materials Science and Engineering.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2003

Author dc:creator

• Allred, Clark L. (Clark Lane), 1972-

Advisor dc:contributor.advisor

• Jeffrey T. Borenstein.

• Materials Science and Engineering.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/29965

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/29965