In this study, $Ni_48Cr_40Fe_12$ thin film was first tried as a new sensing material for thin film strain gage. To verify the possibility of $Ni_48Cr_40Fe_12$ thin film as a strain gage, it was needed first to find out whether its use was proper or not. So, indirect one-patch $Ni_48Cr_40Fe_12$ thin film strain gage was fabricated as a middle step before fabricating direct thin film strain gage.
$Ni_48Cr_40Fe_12$ thin film was not etched by various etchants. But HCl could etch $Ni_48Cr_40Fe_12$ thin film more or less even though its etch rate was very low. In addition, with the AES(Auger Electron Spectroscopy) and EDS analyses, it was found that the element chromium did form oxide on the surface of $Ni_48Cr_40Fe_12$ thin film that made it difficult to etch $Ni_48Cr_40Fe_12$ thin film.
With HCl and the $FeCl_3$ used for etching foil type strain gage, the key idea could be made for fabricating strain gage, that was the passivation of $Ni_48Cr_40Fe_12$ thin film to prevent chromium element from being bonded with oxygen-oxidation and Cu layer was deposited on the $Ni_48Cr_40Fe_12$ thin film as the passivation layer. And also another unique $Ni_48Cr_40Fe_12$ thin film property was found. It was a relatively long sidewall occupying some portions near line patterns. Because each element consisting of thin film had a different etch rate for etchant, this sidewall was inevitably accompanied.
Fabricated one-patch $Ni_48Cr_40Fe_12$ thin film strain gage showed following results. First, gage properties in a same pattern size for each 120 ㎛, 40 ㎛, and 20 ㎛ were improved as HCl concentration increased. And the degree of improvement was the largest in 120 ㎛. This reason could be explained by investigating sidewalls with the SEM analyses. According to the SEM analyses, the geometric structure of sidewalls was characterized by two factors, the size of island type grain and the gap between island type grains. Because these two factors made a strain gage output unstable by switching electrical states between contact and non-contact, the strain gage showed improved properties as the decrease of grain size and grain gap. With the SEM analyses, it was found that the grain size and grain gap decreased as HCl concentration increased. Second, gage properties improved as gage pattern size decreased. This could be explained with the respect of strain sensitivity. However, 40 ㎛ strain gage showed little better properties than 20 ㎛ strain gage because the portion of a sidewall affecting on unstable gage was gage was over-increased as gage pattern decreased, that is, from 40 ㎛ to 20 ㎛
