A thin film transistor composition comprising: A) a semiconductor material; B) a substrate, having a first surface on the side of the substrate closest to the semiconductor material and a second surface on the other side of the substrate and having a thickness from 5 to 150 μm, the substrate comprising: a) a polyimide derived from: i) at least one aromatic dianhydride component selected from the group consisting of rigid rod dianhydride, non-rigid rod dianhydride and combinations thereof, and ii) at least one aromatic diamine component selected from the group consisting of rigid rod diamine, non-rigid rod diamine and combinations thereof; wherein the mole ratio of dianhydride to diamine is 48-52:52-48 and the ratio of X:Y is 35-65:65-35 where X is the mole percent of rigid rod dianhydride and rigid rod diamine, and Y is the mole percent of non-rigid rod dianhydride and non-rigid rod diamine based upon the total dianhydride component and total diamine component of the polyimide; and b) a sub-micron filler: i) being less than 550 nanometers (as a numerical average) in at least one dimension; ii) having an aspect ratio greater than 3:1; iii) being less than the thickness of the substrate in all dimensions; and iv) being present in an amount from 10 to 45 volume percent of the substrate. A) a semiconductor material; B) a substrate, having a first surface on the side of the substrate closest to the semiconductor material and a second surface on the other side of the substrate and having a thickness from 5 to 150 μm, the substrate comprising: a) a polyimide derived from: i) at least one aromatic dianhydride component selected from the group consisting of rigid rod dianhydride, non-rigid rod dianhydride and combinations thereof, and ii) at least one aromatic diamine component selected from the group consisting of rigid rod diamine, non-rigid rod diamine and combinations thereof; wherein the mole ratio of dianhydride to diamine is 48-52:52-48 and the ratio of X:Y is 35-65:65-35 where X is the mole percent of rigid rod dianhydride and rigid rod diamine, and Y is the mole percent of non-rigid rod dianhydride and non-rigid rod diamine based upon the total dianhydride component and total diamine component of the polyimide; and b) a sub-micron filler: i) being less than 550 nanometers (as a numerical average) in at least one dimension; ii) having an aspect ratio greater than 3:1; iii) being less than the thickness of the substrate in all dimensions; and iv) being present in an amount from 10 to 45 volume percent of the substrate. a) a polyimide derived from: i) at least one aromatic dianhydride component selected from the group consisting of rigid rod dianhydride, non-rigid rod dianhydride and combinations thereof, and ii) at least one aromatic diamine component selected from the group consisting of rigid rod diamine, non-rigid rod diamine and combinations thereof; wherein the mole ratio of dianhydride to diamine is 48-52:52-48 and the ratio of X:Y is 35-65:65-35 where X is the mole percent of rigid rod dianhydride and rigid rod diamine, and Y is the mole percent of non-rigid rod dianhydride and non-rigid rod diamine based upon the total dianhydride component and total diamine component of the polyimide; and i) at least one aromatic dianhydride component selected from the group consisting of rigid rod dianhydride, non-rigid rod dianhydride and combinations thereof, and ii) at least one aromatic diamine component selected from the group consisting of rigid rod diamine, non-rigid rod diamine and combinations thereof; b) a sub-micron filler: i) being less than 550 nanometers (as a numerical average) in at least one dimension; ii) having an aspect ratio greater than 3:1; iii) being less than the thickness of the substrate in all dimensions; and iv) being present in an amount from 10 to 45 volume percent of the substrate. i) being less than 550 nanometers (as a numerical average) in at least one dimension; ii) having an aspect ratio greater than 3:1; iii) being less than the thickness of the substrate in all dimensions; and iv) being present in an amount from 10 to 45 volume percent of the substrate.