Dynamic Random Access Memory (DRAM) integrated circuits or chips are the basis for much of the computer memory applications that are presently used worldwide. These important chips are being fabricated, studied and advanced by many manufacturers. The basic device consists of a transistor and a capacitor with associated read and write connections. Information is stored in the charge state of the capacitor which has to be periodically refreshed due to leakage. The most advanced DRAM circuit under production is the 256 MBit chip which in one version uses a trench capacitor with a silicon oxide-nitride-oxide (O-N-O) sandwich with a dielectric constant of about 4. The dielectric thickness is about 7 nm. The deep trenches are slow and relatively expensive to build and much work is devoted to alternative technologies. In addition future, denser DRAM circuits will require even thinner dielectrics and electron tunneling limits will be approached. A great deal of effort around the world is being devoted to alternate dielectric materials with high dielectric constants and alternate or modified structures. With such developments it is expected that trenches can be avoided.
Many high dielectric constant materials are known and some are being investigated for DRAM application. Even with high dielectric constant materials, dielectric thicknesses less than 100 nm may be anticipated. These materials include strontium titanate (STO) and barium titanate (BTO) and their mixtures. Dielectric constants range from a few hundred to over 800 for films of these well-known materials. Mixtures of lead zirconium titanate (PZT) and lead lanthanum titanate (PLT) are also possible high dielectric materials. When these materials are used, they are generally deposited on a base electrode of Pt.
USPTO Backgrounds
USPTO Backgrounds