Patent GB-1366575-A (GB)
Title: Electronic device and method of fabrication
IPC: H01L29/768
Filed: 1972-04-04
Abstract: 1366575 Semi-conductor storage devices TEXAS INSTRUMENTS Inc 4 April 1972 [1 April 1971] 15362/72 Heading H1K A charge coupled storage device (Figs. 1, 3) comprises a semi-conductor, e.g. n-silicon substrate 10 overlain by insulant, e.g. SiO 2  layer 12 covered by overlapping mutually insulated metal electrodes 16, 18 respectively supplied with clock pulses # 1 , # 2 , # 3 , # 4  (Fig. 5) phased #/2 from voltage source 20. Charges are inserted from source 24 through PN junction or modulated light source 22 and are detected at 26 by PN junction or Schottky barrier 28; the position of the inserted charges being controlled by the clock pulses by underlying charge migration. The electrodes longitudinally overlie a thin region of the insulant layer (Fig. 2, not shown) and mutually overlap laterally (Fig. 3). Parallel spaced electrodes 16a &c. are insulatedly anodized at 30 and separated by parallel spaced overlying electrodes 18a &c. The electrodes are of, e.g. Al, Ti, Ta and alternate electrodes 16 are group connected to # 1 , # 3  respectively while alternate interposed electrodes 18 are group connected to # 2 , # 4  respectively (Fig. 4, not shown), and in the anodization process the electrodes 16 are deposited with connecting bus-bars and extensions contacting the semiconductor substrates; the connections being subsequently removed (Fig. 6, not shown). In fabrication a SiO 2  layer 46 overlies a P or N Si substrate 44 and is apertured at 48 for a contact to the substrate, serving to inject or detect the charge through PN or Schottky junctions. A first layer of metal is deposited on the insulant layer, patterned to form electrodes 52 and is covered with an evaporated layer of Al 54. The latter is patterned to define bus-bar 56 and the first series of electrodes (Fig. 7c) and a photoresist layer 58 overlies the connection hole 48 and the required contact points of the aluminium layer, which is electrolytically anodized at 60 by current applied over bus-bar 56. This subsequently converted entirely to the oxide, so arresting the anodization process (Fig. 7d). The photoresist 58 is removed and a further layer of aluminium is evaporated on and patterned to form the second interleaved set of electrodes 62 (Fig. 7e); electrical connections being made to substrate 44 through hole 48, and also to electrodes 52. In a modified method, a thick layer of Al is evaporated on to overlie the insulating layer, patterned to form a bus-bar and first electrodes, photoresist masked to protect the substrate connection, and anodized to form an oxide layer on the aluminium; after which a photoresist layer is applied to all but the bus-bar, which is completely anodized to oxide. Thereafter the layer is removed and a further Al layer evaporated on to form the second electrode series (Figs. 8a- 8c, not shown). In a further modified method, a layer of Al is applied to overlay the insulant, patterned to form a bus-bar, a contact to the substrate, and a first electrode series. A photoresist layer overlies the bus-bar and the substrate contact aperture, and the exposed Al is anodized. After removal of the photoresist the bus-bar is etched out and a further Al layer applied, which is patterned and etched to define the second electrode series and a contact to the substrate (Figs. 9a-9f, not shown). The bus-bar may be etched out together with the underside parts of the second electrode layer (Figs. 10a to 10e, not shown). An interdigited surface wave transducer (Fig. 11, not shown) comprises 1st and 2nd series of spaced interdigitated electrodes formed in the manner described on a piezoelectric substrate of, e.g. quartz, lithium niobate. A signal applied to the electrodes generates a surface wave in the substrate surface.