Logic gates realized with spin dependent tunneling elements
The magnetoresistive effects are considered to improve existing electronic devices. The experimental feasibility of different concept's basic logic gates based on micron sized spin dependent tunneling (SDT) elements is verified, where the emphasize is put on field programmable spin-logic gates.
The thesis is organized as follows. First, the physical principles of spin dependent tunneling which are important for logic are reviewed. Then the principle of digital logic based on SDT elements is explained. Beside the discusssion of concepts known from literature, new concepts are introduced. The feasibility of mask programmable and field programmable logic gates based on SDT elements with a minimal feature of 600 nm is shown.
Characteristics of single SDT elements with impact on logic gates are investigated. The in-plane switching behavior of SDT element's soft magnetic (storage) layer is investigated for different shapes and aspect ratios down to a width of 600 nm. A systematic study on so-called astroids of micron-sized SDT elements is presented. Magnetostatic interactions of the magnetic layers within SDT elements are identified from these measurements.
For spin-logic gates, critical factors for working logic gates are identified. The measured statistical fluctuations of the resistance-area product and tunneling magnetoresistance of the SDT elements forming a spin-logic gate are measured and the corresponding yield of working spin-logic gates is calculated. Furthermore, the benefit of the introduction of a reference layer system which is switchable (programmable) by a current on chip is discussed. Concretely, the reference layer system Ru/CoFe is investigated. The physical origin of the increase of the CoFe coercivity with increasing thickness of the Ru-buffer is investigated. Finally, the magnetic stability, which is a prerequisite for a working spin-logic, is investigated for different designs of the tunneling stack.
Bielefeld University
application/pdf