*Article* **Integrated Piezoresistive Normal Force Sensors Fabricated Using Transfer Processes with Stiction Effect Temporary Handling**

**Ni Liu <sup>1</sup> , Peng Zhong 2,3 , Chaoyue Zheng 2,3, Ke Sun <sup>2</sup> , Yifei Zhong 1,\* and Heng Yang 2,3,\***


**Abstract:** Tactile sensation is a highly desired function in robotics. Furthermore, tactile sensor arrays are crucial sensing elements in pulse diagnosis instruments. This paper presents the fabrication of an integrated piezoresistive normal force sensor through surface micromachining. The force sensor is transferred to a readout circuit chip via a temporary stiction effect handling process. The readout circuit chip comprises two complementary metal-oxide semiconductor operational amplifiers, which are redistributed to form an instrumentation amplifier. The sensor is released and temporarily bonded to the substrate before the transfer process due to the stiction effect to avoid the damage and movement of the diaphragm during subsequent flip-chip bonding. The released sensor is pulled off from the substrate and transferred to the readout circuit chip after being bonded to the readout circuit chip. The size of the transferred normal force sensor is 180 µm × 180 µm × 1.2 µm. The maximum misalignment of the flip-chip bonding process is approximately 1.5 µm, and sensitivity is 93.5 µV/µN/V. The routing of the piezoresistive Wheatstone bridge can be modified to develop shear force sensors; consequently, this technique can be used to develop tactile sensors that can sense both normal and shear forces.

**Keywords:** complementary metal-oxide semiconductor; MEMS; tactile sensor; stiction effect; temporary handling; stiction contact; Au–Si eutectic; flip-chip
