In a disc apparatus, a tray gear has a boss protruding from one predetermined place in an inner circumference edge part thereof. The materials and processes used enable self-alignment of elements of the buried bit line during the fabrication process. The common source stage, following the source follower stage, driven by the reduced signal source impedance, amplifies the current signal to extend a frequency bandwidth of the current signal and buffers the amplified signal with the extended frequency bandwidth thereof maintained, wherein the reduced signal source impedance serves to extend a frequency bandwidth of the common source stage. This removaldesignation can include accessing a desired layout and expanding layout features only in directions along critical dimensions of those layout features.