Polyamide-imide-based film, preparation method thereof, and cover window and display device comprising the same

A display device, which comprises a display unit;

• and a cover window disposed on the display unit,
• wherein the cover window comprises a polyamide-imide-based film and a functional layer, the polyamide-imide-based film comprises a polyamide-imide-based polymer,
• wherein when the coefficients of thermal expansion in the MD direction and TD direction of the polyamide-imide-based film are measured at an interval of 5° C. in a temperature range of 300° C. to 365° C., respectively, the temperature at which the coefficient of thermal expansion in the MD direction or the coefficient of thermal expansion in the TD direction changes from a positive value to a negative value is 330° C. to 345° C., and
• wherein when the haze is measured at six points in total, in which two arbitrary points are selected in each of region N, region C, and region S partitioned in the TD direction of the film, the average value of haze is 1% or less, and the deviation rate of haze is 10% or less.