#homecmos IRC log for Monday, 2011-08-08

kristianpaulwhat is your comb-drive ref?01:17
kristianpauls/ref/specs01:18
azonenbergMy tentative plan calls for it to be made from <110> Si wafer, 15-30 microns high, 20 micron wide fingers01:20
azonenbergBut that depends on the aspect ratios i'm able to hit experimentally01:21
azonenbergIf i'm lucky i could potentially get like a 10:1 aspect ratio which would permit 200um high fingers01:21
azonenbergother papers have done that01:21
azonenbergit depends really on how well my hardmask sticks to the wafer and how well it survives exposure to KOH01:21
azonenbergRight now sol-gel Ta2O5 appears to fill both of those very well01:21
azonenbergits almot impossible to remove, the "scotch tape test" doesnt damage the film whatsoever01:22
azonenbergAnd its etch rate in KOH according to several publications is usper low01:22
azonenbergusper*01:22
azonenbergsuper*01:22
azonenberglike angstroms per year01:22
azonenbergeffectively zero01:22
azonenbergAnd now that i've almost solved the problem of patterning it, i should get very good results01:22
azonenberg44% KOH is extremely anisotropic - the etch rate of <110> is around 600 times that of <111> planes01:25
azonenbergSo 100:1 aspect ratios are potentially feasible01:26
azonenbergthat's on par with deep RIE01:26
azonenbergBut i havent seen any literature using KOH for more than around 10:1 or 15:101:26
azonenbergIt really seems that KOH is a near-ideal etchant because it's fast, gives relatively smooth surfaces if you use it right, and is extremely selective01:31
azonenbergthe only downside is metal ions which are a problem for CMOS but not MEMS01:31
azonenbergAnd while it's pretty fast it still will take a bit over 2.5 hours to do the 500um etch i need lol01:32
Action: azonenberg wonders if he should have gotten thinner wafers to start with01:33
XgFI guess slow etchants are one of the reasons why foundries like big wafers?01:33
azonenbergYou think that's slow? Lol01:34
azonenbergXeF2 will take overnight to go this fart01:34
azonenbergfar*01:34
azonenbergBut it doesnt have metal ions and is therefore CMOS compatible01:34
azonenbergBut yes01:34
azonenbergIt costs about the same amount to process a big wafer or a small one01:34
azonenbergbut they make more money with big ones01:34
XgFOn a commercial scale, I bet thats a bottleneck :p01:34
azonenbergLol yeah01:35
azonenberghttp://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=471727501:59
azonenbergvery interesting paper describing fabrication of MEMS micromirrors01:59
azonenbergthe mirror is on a <110> plane01:59
azonenberg<111>*01:59
azonenbergand is produced by a KOH etch of a <110> wafer01:59
bart416azonenberg, electron gun assembly from crt extracted12:11
Laurencebnice12:14
bart416Still need to cut the glass all the way down12:17
bart416But considering how to best do that12:17
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