My PhD project in the late ’70s involved the development of Indium-Tin-Oxide (ITO) CCD electrodes.\u00a0 ITO is a transparent and conductive material, from the standpoint of view of those characteristics, ITO is ideally suited to be used as a CCD electrode.\u00a0 In the first year of my research, I succeeded in the deposition of transparent ITO that was fully oxidized, and was actually non conductive.\u00a0 By means of an appropriate anneal the ITO films could be made conductive as well.\u00a0 Actually what was realized was a kind of conductive glass.<\/p>\n
In the second year of my PhD project (= 40 years ago) I focused on using the ITO film as a gate electrode in a MOS structure.\u00a0 And that turned out to be much more difficult than expected.\u00a0 I still remember that I had to set up a measurement system to perform HF and LF capacitance measurements on the realized MOS capacitor with the ITO top gate.\u00a0 A hard copy of the developed software code in Fortran is still present in my archives.\u00a0 Unfortunately the RF sputtering technique applied to deposit the ITO films created too much radiation damage in the MOS structures.\u00a0 As a result, the MOS capacitors showed a very high number of surface states.\u00a0 A high number of surface or interface states would ultimately result in a very high dark current in the final CCDs.\u00a0 Too bad !\u00a0 I tried many annealing methods, various annealing atmospheres in combination with various temperatures, but none of them resulted in a low number of surface states.\u00a0 I still remember that\u00a0 I worked in close cooperation with the solar cell R&D team.\u00a0 They offered me the opportunity to anneal my “dirty” structures in their furnaces at high temperatures, even in a reactor in which the structures could be annealed in hydrogen.\u00a0 But no processing recipe could be found that resulted in a low number of surface states.\u00a0 So the only solution was to give up the damaging RF sputter technique and to make use of magnetron sputtering for deposition of the ITO films.\u00a0 Magnetron sputtering was known to result in a low level of radiation damage and seemed to be suited for deposition of gate material on MOS structures.<\/p>\n
I remember that the university was willing to buy a new magnetron sputtering system from Balzers.\u00a0 But Balzers was not really familiar with the sputtering of ITO, so I had to go to the company in Liechtenstein to perform ITO experiments.\u00a0 This was my very first business trip ever, all the way flying to Zurich and then the train to Sargans if I recall well.\u00a0 Once at Balzers’facility we succeeded immediately to deposit the right combination of Indium Oxide and Tin Oxide, so we gave a\u00a0“go” to buy the machine.\u00a0 It was Mr. Klinkemay of Balzers (probably misspelled ?!) who did the installation of the machine in our laboratory at the university.\u00a0 Also with the final machine the first films of ITO were realized very quickly.\u00a0 So ready to deposit ITO films with a low level of radiation damage !\u00a0 My work with the magnetron sputter machine became so well accepted in the lab, that the machine was provided with a second aluminum target and the machine was going to be used in our lab as the “standard” deposition method for aluminum metallization of integrated circuits.\u00a0 As a result, I almost had to beg on my bare knees to use my “own” machine for the ITO depositions.\u00a0 After a while the management of the lab saw the problems, and decided to buy a second machine.\u00a0 What a luxury, I got my own machine back for my own ITO depositions !\u00a0 An incredible amount of test MOS capacitors were deposited, annealed and measured.\u00a0 A Russian postdoc helped me out with the measurements (unfortunately I lost his name).\u00a0 And yes, finally we succeeded in realizing MOS capacitors with an ITO gate material that showed a low number of surface states, not as low as a capacitor with a poly-silicon gate, but more than an order of magnitude less than the devices fabricated with the RF sputter machine.\u00a0 A major step forward !<\/p>\n
Albert, 14-11-2019.<\/p>\n","protected":false},"excerpt":{"rendered":"
My PhD project in the late ’70s involved the development of Indium-Tin-Oxide (ITO) CCD electrodes.\u00a0 ITO is a transparent and conductive material, from the standpoint of view of those characteristics, ITO is ideally suited to be used as a CCD electrode.\u00a0 In the first year of my research, I succeeded in the deposition of transparent […]<\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[],"class_list":["post-1773","post","type-post","status-publish","format-standard","hentry","category-uncategorized"],"_links":{"self":[{"href":"https:\/\/harvestimaging.com\/blog\/index.php?rest_route=\/wp\/v2\/posts\/1773","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/harvestimaging.com\/blog\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/harvestimaging.com\/blog\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/harvestimaging.com\/blog\/index.php?rest_route=\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/harvestimaging.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=1773"}],"version-history":[{"count":1,"href":"https:\/\/harvestimaging.com\/blog\/index.php?rest_route=\/wp\/v2\/posts\/1773\/revisions"}],"predecessor-version":[{"id":1774,"href":"https:\/\/harvestimaging.com\/blog\/index.php?rest_route=\/wp\/v2\/posts\/1773\/revisions\/1774"}],"wp:attachment":[{"href":"https:\/\/harvestimaging.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=1773"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/harvestimaging.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=1773"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/harvestimaging.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=1773"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}