A tunable filter device, comprising: a substrate; and a plurality of horizontal gap closing actuator, GCA, devices (600; 700) disposed on a first surface of said substrate, wherein each one of said plurality of horizontal GCA devices (600; 700) comprises at least one drive comb structure (602a, 602b, 702a, 702b), at least one input/output, I/O, comb structure (616a, 616b, 716a, 716b) separated and electrically isolated from said drive comb structure (602a, 602b, 702a, 702b), and at least one truss comb structure (604, 704) interdigitating said drive comb and said I/O comb structures, said truss comb structure (604, 704) being configured to move along a motion axis (605, 705) between a first interdigitated position and at least a second interdigitated position based on a bias voltage (V BIAS) applied at a bias port between said truss comb structure (604, 704) and said drive comb structure (602a, 602b, 702a, 702b), wherein, in the first interdigitated position, an interdigital spacing (X 0_REACT) between said truss comb structure and said I/O comb structure (716a, 716b) is the same as or greater than the interdigital spacing (X 0_DRV) between said truss comb structure and said drive comb structure (702a, 702b) in at least a first one of said horizontal GCA devices in which said I/O comb structure is configured as part of a varactor between said input/output I/O comb structure (716a, 716b) and said truss comb structure, characterised in that in the first interdigitated position, an interdigital spacing (X 0_REACT) between said truss comb structure and said I/O comb structure (616a, 616b) is the same as or smaller than the interdigital spacing (X 0_DRV) between said truss comb structure and said drive comb structure (602a, 602b) in at least a second one of said horizontal GCA devices to facilitate electrical contact between said I/O comb structure (616a, 616b) and said truss comb structure in the second interdigitated position, whereby said second one of said horizontal GCA devices is configured to function as a switch at a switch port between said input/output I/O comb structure (616a, 616b) and said truss comb structure, wherein at least said first one of said horizontal GCA devices comprises a stopper configured to limit an amount of motion of said truss comb structure (204, 704, 704) and prevent at least said interdigital spacing between said truss comb structure and said I/O comb structure (616a, 616b) from going to zero, and wherein the truss comb structure (204, 604, 704) presents a discontinuity (624, 724) so as to separate and electrically isolate the part interdigitating the drive comb structure (602a, 602b, 702a, 702b) and the part interdigitating the I/O comb structure (616a, 616b, 716a, 716b). a substrate; and a plurality of horizontal gap closing actuator, GCA, devices (600; 700) disposed on a first surface of said substrate, wherein each one of said plurality of horizontal GCA devices (600; 700) comprises at least one drive comb structure (602a, 602b, 702a, 702b), at least one input/output, I/O, comb structure (616a, 616b, 716a, 716b) separated and electrically isolated from said drive comb structure (602a, 602b, 702a, 702b), and at least one truss comb structure (604, 704) interdigitating said drive comb and said I/O comb structures, said truss comb structure (604, 704) being configured to move along a motion axis (605, 705) between a first interdigitated position and at least a second interdigitated position based on a bias voltage (V BIAS) applied at a bias port between said truss comb structure (604, 704) and said drive comb structure (602a, 602b, 702a, 702b), wherein, in the first interdigitated position, an interdigital spacing (X 0_REACT) between said truss comb structure and said I/O comb structure (716a, 716b) is the same as or greater than the interdigital spacing (X 0_DRV) between said truss comb structure and said drive comb structure (702a, 702b) in at least a first one of said horizontal GCA devices in which said I/O comb structure is configured as part of a varactor between said input/output I/O comb structure (716a, 716b) and said truss comb structure, characterised in that in the first interdigitated position, an interdigital spacing (X 0_REACT) between said truss comb structure and said I/O comb structure (616a, 616b) is the same as or smaller than the interdigital spacing (X 0_DRV) between said truss comb structure and said drive comb structure (602a, 602b) in at least a second one of said horizontal GCA devices to facilitate electrical contact between said I/O comb structure (616a, 616b) and said truss comb structure in the second interdigitated position, whereby said second one of said horizontal GCA devices is configured to function as a switch at a switch port between said input/output I/O comb structure (616a, 616b) and said truss comb structure, wherein at least said first one of said horizontal GCA devices comprises a stopper configured to limit an amount of motion of said truss comb structure (204, 704, 704) and prevent at least said interdigital spacing between said truss comb structure and said I/O comb structure (616a, 616b) from going to zero, and wherein the truss comb structure (204, 604, 704) presents a discontinuity (624, 724) so as to separate and electrically isolate the part interdigitating the drive comb structure (602a, 602b, 702a, 702b) and the part interdigitating the I/O comb structure (616a, 616b, 716a, 716b).