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Despite the increasingly significant role of flexible electronics in information, energy, and medical treatment, their integration with a special‐shaped interface remains an unresolved challenge. The traditional transfer method, as a core technology of device integration, is still unsuitable for thinned chips and 3D sensors. Solid‐contact elastomer stamp sometimes causes cracks while non‐contact method such as sacrificial layer method fails to achieve precise positioning transfer. Herein, the authors present liquid droplet stamp transfer printing (LSTP) with a high yield ratio which allows flexible devices to be transferred form silicon wafer to complex special‐shaped interfaces. Following the transfer scheme, the regulation of interface force is demonstrated with different thin‐film patterns. Besides, the liquid droplet stamp is designed as an efficient tool to transfer thinned inorganic flexible chips. A thinned micro light emitting diode, extensively used in large‐scale manufacturing of flexible circuits, is transferred and lighted successfully. In addition, a new method to fabricate 3D sensors is proposed with the liquid droplet stamp, which provides a new way of manufacturing wearable antenna and reconfigurable devices. Consequently, the LSTP has great potential for future sophisticated and system‐level flexible devices transfer printing and plays a vital role in the research of 3D flexible electronics.

This paper presents a fully integrated C-band Doherty power amplifier (DPA) based on a 0.25-µm GaN-HEMT process for the 5G massive MIMO application. The performance degradation caused by nonlinear output capacitance is analyzed, and a novel compensation technique is proposed. A low-Q output network is employed to broaden the bandwidth, and its insertion loss in the back-off region is demonstrated to be mainly decided by the Q-factor of the drain bias inductor of the main PA. Hence, by adopting on-chip transmission lines with high Q-factors for drain biasing, a full integration, and a low loss can be achieved simultaneously. Reversed uneven power splitting and back-off input matching are proposed for gain enhancement. The fabricated DPA demonstrates a small-signal gain of 8.6-11.6 dB, an output power of 40.4-41.2 dBm, a 6-dB back-off drain efficiency (DE) of 47%-50%, and a saturation DE of 55%-63% across a wide bandwidth from 4.5 to 5.2 GHz, with an ultra-compact size of 2.2 mm × 2.1 mm. Using a 40-MHz LTE signal with a 7.7-dB peak-to-average power ratio at the carrier frequency of 4.9 GHz, the measured average output power and efficiency are 33 dBm and 43%, respectively. The raw adjacent channel power ratio is −29 dBc and is improved to −46 dBc by applying digital predistortion. INDEX TERMS Doherty power amplifier (DPA), fully integrated, 5G, gallium-nitride (GaN), high-efficiency, monolithic microwave integrated circuit (MMIC).