Patent GB-1375063-A (GB)
IPC: G11C19/28
Filed: 1972-02-21
Abstract: 1375063 Charge coupled devices INTERNATIONAL BUSINESS MACHINES CORP 21 Feb 1972 [29 March 1971 (2)] 7896/72 Heading H1K In a charge coupled device the charge is transferred along a serpentine path in the substrate by means of a two-phase supply applied to electrodes comprising a pair of fingered structures arranged so that the transfer path is completely covered by the combination of the fingers of the electrodes. As shown, Fig. 1, an N-type Si wafer 10 is provided with a thick SiO 2  layer which is processed to form ridges 11, and thin insulating layers 14 are formed in the troughs 12 which form the charge transfer paths. A layer of conductive material, e.g. Al, Ag or heavily doped Si is deposited and selectively etched to form a plurality of spaced plates 15 in each trough, the plates in adjacent troughs being staggered. A layer 16 of SiO 2  or Si 3 N 4  is deposited and apertures are formed to expose a portion of each plate 15. A layer of Al is then deposited and etehed to form conductive strips 18 which extend transversely to the ridges 11 in such a way that in each trough they overlap the spaces between a pair of adjacent plates 15 and extend through an aperture in the insulating layer 16 to contact one of these plates. The staggered arrangement of the plates 15 enables the conductive strip to be connected to alternately disposed plates in adjacent troughs so that the charges are shifted in opposite directions. The ends of adjacent troughs can be coupled to form a folded track shift register.  In a second embodiment, Figs. 6 to 8 (not shown), the thick insulation ridges are arranged to provide pairs of closely spaced troughs separated by greater distances from adjacent pairs, the lower parts of the electrodes are in the form of zig-zag tracks which cross each pair of troughs perpendicularly and are then bent to cross the adjacent pairs of troughs at points staggered relative to the first crossing point. A layer of insulating material covers these tracks and is provided with apertures through which upper electrode strips extending perpendicularly to the thick ridges contact the lower tracks. The upper strips overlap the spaces between adjacent lower electrode tracks within the troughs and the arrangement is such that charge transport is in the same direction in both of the members of each pair of closely spaced troughs but in opposite directions in adjacent pairs of troughs. The ends of one trough of a pair may be coupled to those of the trough in the adjacent pair to form a circulating shift register. The thin insulating layer on the floor of each trough may comprise a layer of SiO 2  covered with a layer of Si 3 N 4 . Alternatively this insulation may be Al 2 O 3 , AlN or BeO. In a further embodiment, Figs. 9 to 13 (not shown), thick ridges of SiO 2  are formed on a Si wafer, a layer of oxide of medium thickness is formed in the troughs and openings are etched, and the exposed parts of the surface are covered with a thin oxide layer. A metal, e.g. Cr, or Mo is then applied by sputtering to form conductive layers on the top surfaces of all the oxide layers but not on the vertical surfaces joining them. The conductive layers on the thick ridges of oxide are then etched off so that within each trough self-aligned electrode plates are provided which are alternately separated from the surface by the thin and medium thickness oxide layers, the relative positions being alternated (staggered), in adjacent troughs. A layer of Al is deposited over the surface and etched using an etchant which wil not attack the conductive plates (Mo or Cr) to form conductive strips extending perpendicularly to the thick oxide ridges and overlapping adjacent pairs of electrode plates to form twolevel electrodes.  The charge is shifted in opposite directions in adjacent troughs becuase of the staggered arrangement of the electrode plates. Contact wires may be thermocompression bonded to one end of each conductive strip and a thick film of quartz may be sputtered over the electrodes and connections. Si 3 N 4 , Al 2 O 3 , AlN or BeO may be used instead of SiO 2 .