To improve the optical performance of the conformal white light-emitting diodes (LEDs), previous studies mainly focus on the phosphor structures design by simulations and experiments methods. However, one of the most critical parameters, i.e., the height of chips, is barely studied. In this study, we have experimentally investigated the effect of the flip-chip height on the optical performance of conformal white LEDs. The results show that larger chip height can cause lower radiant power and luminous flux, while wider viewing angles can be achieved. By selecting a suitable chip height of 200 μm, superior color uniformity for white LEDs can be obtained with only 168 K correlated color temperature ($\mathrm{\Delta }\mathrm{CCT}$). This study can provide a new perspective to improve the color uniformity without changing the phosphor structures or using special scattering elements; moreover, it can facilitate the selection of a proper chip height, considering different illumination requirements. Further investigations on the chip height considering packaging structures are still necessary to improve the luminous flux and the color uniformity simultaneously.

中文翻译：

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倒装芯片高度对保形白色发光二极管光学性能的影响

为了提高共形白色发光二极管（LED）的光学性能，以往的研究主要集中在通过模拟和实验方法来设计荧光粉结构上。但是，几乎没有研究最关键的参数之一，即切屑的高度。在这项研究中，我们通过实验研究了倒装芯片高度对共形白色LED光学性能的影响。结果表明，较大的芯片高度可以导致较低的辐射功率和光通量，同时可以实现更宽的视角。通过选择200μm的合适芯片高度，只需168 K的相关色温即可获得白色LED的出色色彩均匀性（$\mathrm{\Delta }\mathrm{色温}$）。这项研究可以提供一个新的视角，以改善色彩均匀性而无需改变荧光粉的结构或使用特殊的散射元素。此外，考虑到不同的照明要求，它可以帮助选择合适的芯片高度。仍需要对考虑封装结构的芯片高度进行进一步研究，以同时提高光通量和颜色均匀性。