Beam focusing characteristics of silicon microtips with an in-plane lens

Single microtips, 2×2 and 10×10 arrays of microtips surrounded by an integrated focusing ring, were fabricated and their focusing characteristics experimentally investigated. Observation of the beam on a phosphor screen shows that the focusing is very effective for single microtips and 2×2 arrays; moreover, the reduction in emitted current is much smaller than for double-gate focusing. 10×10 arrays of microtips, however, do not generate very focused beams. These results agree well with simulations. The possibility of simultaneous focusing and deflecting is also discussed, and a new structure combining the advantages of double-gate and surrounding ring focusing is suggested