Mechanical separators and screening machines, and methods for flexible sieve mat screening are disclosed. Electron beams emitted from electron emission elements of a multi-electron beam generating unit receive the lens effect of a lens electrode. Accordingly, the nickel-gold plating achieves a high resistance to corrosion with little impairment of production cost or productivity. The storage node contacts traverse through the interlayer dielectric layer and are electrically coupled to their respective landing plug contacts.