Abstract: A worm reducer has: a housing having a wheel housing portion and a worm housing portion; a worm wheel; a worm, a support bearing having an inner ring externally fitted to the tip end portion of the worm and an outer ring; an elastic biasing means elastically biasing the outer ring toward the worm wheel side; and an elastic holding means elastically holding the outer ring from both sides in a direction orthogonal to a biasing direction by the elastic biasing means and to a center axis of the worm housing portion.

Abstract: A worm reduction gear, including: an inner diameter side holder in which a bearing is internally fitted and held; an outer diameter side holder which includes a holder holding part in which the inner diameter side holder is internally fitted and held so as to be able to be relatively rotated and moved and to be displaced in a direction orthogonal to a center axis of a worm wheel and a center axis of a worm, and which is internally fitted and held in a holding recessed part of a housing; and an elastic urging member in a circumferential direction which elastically urges the inner diameter side holder against the outer diameter side holder in a direction of rotating in the circumferential direction.

Abstract: A worm reducer has: a housing having a wheel housing portion and a worm housing portion; a worm wheel; a worm, a support bearing having an inner ring externally fitted to the tip end portion of the worm and an outer ring; an elastic biasing means elastically biasing the outer ring toward the worm wheel side; and an elastic holding means elastically holding the outer ring from both sides in a direction orthogonal to a biasing direction by the elastic biasing means and to a center axis of the worm housing portion.

Abstract: Disclosed herein is a worm reduction gear, including: an inner diameter side holder in which a bearing is internally fitted and held; an outer diameter side holder which includes a holder holding part in which the inner diameter side holder is internally fitted and held so as to be able to be relatively rotated and moved and to be displaced in a direction orthogonal to a center axis of a worm wheel and a center axis of a worm, and which is internally fitted and held in a holding recessed part of a housing; and an elastic urging member in a circumferential direction which elastically urges the inner diameter side holder against the outer diameter side holder in a direction of rotating in the circumferential direction.

Abstract: Provided are a semiconductor device and a bidirectional field effect transistor which can easily overcome the tradeoff relation between the high voltage resistance and high speed in the semiconductor device using a polarization super junction, realize both the high voltage resistance and elimination of the occurrence of current collapse, operate at a high speed, and further the loss is low. The semiconductor device comprises a polarization super junction region and a p-electrode contact region. The polarization super junction region comprises an undoped GaN layer 11, an undoped AlxGa1-xN layer 12 with a thickness not smaller than 25 nm and not larger than 47 nm and 0.17?x?0.35, an undoped GaN layer 13 and a p-type GaN layer 14. When the reduced thickness tR is defined as tR=u+v(1+w×10?18) for the thickness u [nm] of the undoped GaN layer 13, the thickness v [nm] and the Mg concentration w [cm?3] of the p-type GaN layer 14, tR?0.864/(x?0.134)+46.0 [nm] is satisfied.

Abstract: Provided is a semiconductor element in which a two-dimensional hole gas with an enough concentration can exist, even though the p-type GaN layer is not provided on the topmost surface of the polarization super junction region. The semiconductor element comprises a polarization super junction region comprising an undoped GaN layer 11 with a thickness a [nm] (a is not smaller than 10 nm and not larger than 1000 nm), an AlxGa1-xN layer 12 and an undoped GaN layer 13. The Al composition x and the thickness t [nm] of the AlxGa1-xN layer 12 satisfy the following equation t??(a)x?(a) Where ? is expressed as Log (?)=p0+p1 log (a)+p2{log (a)}2 (p0=7.3295, p1=?3.5599, p2=0.6912) and ? is expressed as ?=p?0+p?1 log (a)+p?2{log (a)}2 (p?0=?3.6509, p?1=1.9445, p?2=?0.3793).

Abstract: Provided are a semiconductor device and a bidirectional field effect transistor which can easily overcome the tradeoff relation between the high voltage resistance and high speed in the semiconductor device using a polarization super junction, realize both the high voltage resistance and elimination of the occurrence of current collapse, operate at a high speed, and further the loss is low. The semiconductor device comprises a polarization super junction region and a p-electrode contact region. The polarization super junction region comprises an undoped GaN layer 11, an undoped AlxGa1-xN layer 12 with a thickness not smaller than 25 nm and not larger than 47 nm and 0.17?x?0.35, an undoped GaN layer 13 and a p-type GaN layer 14. When the reduced thickness tR is defined as tR=u+v(1+w×10?18) for the thickness u [nm] of the undoped GaN layer 13, the thickness v [nm] and the Mg concentration w [cm?3] of the p-type GaN layer 14, tR?0.864/(x?0.134)+46.0 [nm] is satisfied.