Foldable electronic device assemblies and cover elements for the same
A cover element for a foldable electronic device that includes a foldable glass element, first and second primary surfaces, and a compressive stress region extending from the first primary surface to a first depth that is defined by a stress σ I of at least about 100 MPa in compression at the first primary surface. The device also includes a polymeric layer disposed over the first primary surface. The glass element has a stress profile such that when the glass element is bent to a target bend radius of from 1 mm to 20 mm, to induce a bending stress σ B at the first primary surface in tension, σ I +σ B <400 MPa (in tension). Further, the cover element can withstand a pen drop height of at least 1.5 times that of a control pen drop height of the cover element without the layer according to a Drop Test 1.
1. A cover element for a foldable electronic device, comprising:
a foldable glass element comprising a thickness from about 25 μm to about 200 μm the glass element further comprising:
(a) a first primary surface,
(b) a second primary surface, and
(c) a compressive stress region extending from the first primary surface of the glass element to a first depth in the glass element, the region defined by a stress σ I of at least about 100 MPa in compression at the first primary surface of the glass element; and
a polymeric layer comprising a thickness from about 10 μm to about 100 μm and disposed over the first primary surface of the glass element,
wherein the glass element is characterized by a stress profile such that when the glass element is bent to a target bend radius of from 1 mm to 20 mm, with the center of curvature on the side of the second primary surface so as to induce a bending stress σ B at the first primary surface in tension, 0≤σ I +σ B <400 MPa (in tension), and
wherein the cover element comprises an ability to withstand a pen drop height of at least 1.5 times that of a control pen drop height of the cover element without the layer, wherein the pen drop heights are measured according to a Drop Test 1, with the layer disposed on the side of the glass element facing the pen.
2. The cover element according to claim 1 , wherein the stress at the first primary surface of the glass element is from about 700 MPa to about 2000 MPa in compression, and further wherein the compressive stress region comprises a plurality of ion-exchangeable metal ions and a plurality of ion-exchanged metal ions, the ion-exchanged metal ions comprising an atomic radius larger than the atomic radius of the ion-exchangeable metal ions.
3. The cover element according to claim 1 , wherein the first depth is set at approximately one third of the thickness of the glass element or less from the first primary surface of the glass element.
4. The cover element according to claim 1 , further comprising:
a scratch-resistant coating disposed on the polymeric layer,
wherein the coating has a pencil hardness of at least 5H according to ASTM Test Method D3363, and
further wherein the cover element with the layer and the coating comprises an ability to withstand a pen drop height of at least 1.5 times that of a control pen drop height of the cover element without the layer and the coating, wherein the pen drop heights are measured according to a Drop Test 1, with the layer and coating disposed on the side of the glass element facing the pen.
5. The cover element according to claim 1 , wherein the glass element further comprises a maximum flaw size of less than or equal to 2 μm at the first primary surface of the glass element.
6. The cover element according to claim 1 , wherein the layer comprises a polyimide, a polyethylene terephthalate, a polycarbonate or a poly methyl methacrylate.
7. The cover element according to claim 1 , wherein the layer is coupled to the glass element by an adhesive.
8. The cover element according to claim 1 , wherein σ I +σ B <0 MPa at a depth of at least 1 μm below the first primary surface of the glass element.
9. The cover element according to claim 1 , further comprising a scratch-resistant coating disposed on the polymeric layer, wherein the scratch-resistant coating has a pencil hardness of at least 5H according to ASTM Test Method D3363.