Composite membrane, touchpad and display device

A display device, comprising:

• a display module;
• and
• a composite membrane disposed on a light emitting surface side of the display module;
• wherein the composite membrane comprises:
• a first graded-refractive-index layer, a first dielectric layer and a second graded-refractive-index layer which are stacked in sequence;
• wherein the first graded-refractive-index layer comprises at least two first sub-layers, and the second graded-refractive-index layer comprises at least two second sub-layers;
• in a direction from the first graded-refractive-index layer to the first dielectric layer, refractive indexes of first sub-layers in the first graded-refractive-index layer sequentially increase, and refractive indexes of second sub-layers in the second graded-refractive-index layer sequentially decrease;
• a refractive index of a first sub-layer adjacent to the first dielectric layer is less than or equal to a refractive index of the first dielectric layer;
• and
• a refractive index of a second sub-layer adjacent to the first dielectric layer is less than or equal to the refractive index of the first dielectric layer;
• wherein the device further comprising:
• a display region and a non-display region around the display region;
• and
• a second ink layer and a second composite membrane, wherein the second ink layer is disposed in the non-display region and the second composite membrane is disposed in the display region;
• and
• wherein the second ink layer and the display module are disposed on a same side of the composite membrane, and the second composite membrane is disposed between the display module and the composite membrane.