Disclosed are one-port and two-port microelectromechanical structures including variable capacitors, switches, and filter devices. High aspect-ratio micromachining is used to implement low-voltage, large value tunable and fixed capacitors, and the like. Tunable capacitors can move in the plane of the substrate by the application of DC voltages and achieve greater than 240 percent of tuning. Exemplary microelectromechanical apparatus comprises a single crystalline silicon substrate, and a conductive structure laterally separated from the single crystalline silicon substrate by first and second high aspect ratio gaps of different size, wherein at least one of the high aspect ratio gaps has an aspect ratio of at least 30:1, and is vertically anchored to the single crystalline silicon substrate by way of silicon nitride.