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Anisotropic etching of (100) silicon using KOH with 45 • alignment to the primary 110 wafer flat was investigated. It was shown that in KOH solution with isopropyl alcohol added, high KOH concentration and temperature caused the selection of {100} instead of {110} walls, allowing reliable fabrication of {100} walls with improved surface smoothness due to the isopropyl alcohol. TMAOH solutions with methanol and isopropyl alcohol were also found to produce both types of wall, with excellent surface smoothness for the {110} walls. A new maskless etching technique was developed for corner compensation of structures bounded by {110} walls.

Since its first identification in Scotland, over 1000 cases of unexplained pediatric hepatitis in children have been reported worldwide, including 278 cases in the UK 1 . Here we report investigation of 38 cases, 66 age-matched immunocompetent controls and 21 immunocompromised comparator subjects, using a combination of genomic, transcriptomic, proteomic and immunohistochemical methods. We detected high levels of adeno-associated virus 2 (AAV2) DNA in liver, blood, plasma or stool from 27/28 cases. We found low levels of Adenovirus (HAdV) and Human Herpesvirus 6B (HHV-6B), in 23/31 and 16/23 respectively of the cases tested. In contrast, AAV2 was infrequently detected at low titre in blood or liver from control children with HAdV, even when profoundly immunosuppressed.AAV2, HAdV and HHV-6 phylogeny excluded emergence of novel strains in cases. Histological analyses of explanted livers showed enrichment for T-cells and B-lineage cells.Proteomic comparison of liver tissue from cases and healthy controls, identified increased expression of HLA class 2, immunoglobulin variable regions and complement proteins.HAdV and AAV2 proteins were not detected in the livers. Instead, we identified AAV2 DNA complexes reflecting both HAdV and HHV-6B-mediated replication. We hypothesize that high levels of abnormal AAV2 replication products aided by HAdV and in severe cases HHV-6B, may have triggered immune-mediated hepatic disease in genetically and immunologically predisposed children.

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The possibility of using sputtered metals as mask materials for deep anisotropic alkaline etching in silicon was investigated. Sputtered films of chrome, nickel and tungsten were all found to be chemically resistant to potassium hydroxide (KOH) and tetramethyl ammonium hydroxide (TMAOH). However, as expected, these metals had poor adhesion to silicon. By comparison, sputtered titanium was found to have excellent adhesion properties, but was susceptible to chemical attack under some conditions. Titanium was found to be chemically resistant to TMAOH if the solution was kept below 80 • C, and to KOH solution only below 80 • C and with the pH reduced by the addition of a weak acid. An alternative was to thermally oxidize the titanium, in which case it was chemically resistant to KOH and TMAOH under all conditions. However, TiO 2 was found to be more difficult to pattern and remove than titanium.