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Endoscopic optical-coherence tomography (OCT) systems require low cost mirrors with small footprint size, out-of-plane deflections and low bias voltage. These requirements can be achieved with electrothermal actuators based on microelectromechanical systems (MEMS). We present the design and modeling of polysilicon electrothermal actuators for a MEMS mirror (100 μm × 100 μm × 2.25 μm). These actuators are composed by two beam types (2.25 μm thickness) with different cross-section area, which are separated by 2 μm gap. The mirror and actuators are designed through the Sandia Ultra-planar Multi-level MEMS Technology V (SUMMiT V®) process, obtaining a small footprint size (1028 μm × 1028 µm) for actuators of 550 µm length. The actuators have out-of-plane displacements caused by low dc voltages and without use material layers with distinct thermal expansion coefficients. The temperature behavior along the actuators is calculated through analytical models that include terms of heat energy generation, heat conduction and heat energy loss. The force method is used to predict the maximum out-of-plane displacements in the actuator tip as function of supplied voltage. Both analytical models, under steady-state conditions, employ the polysilicon resistivity as function of the temperature. The electrothermal-and structural behavior of the actuators is studied considering different beams dimensions (length and width) and dc bias voltages from 0.5 to 2.5 V. For 2.5 V, the actuator of 550 µm length reaches a maximum temperature, displacement and electrical power of 115 °C, 10.3 µm and 6.3 mW, respectively. The designed actuation mechanism can be useful for MEMS mirrors of different sizes with potential application in endoscopic OCT systems that require low power consumption.

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We present the design and integration of a nine-pH microsensor array on a single silicon substrate with its own signal readout circuit, integrated in a 0.6-μm commercial standard complementary metal oxide semiconductor (CMOS) process. An ion sensitive field effect transistor (ISFET) has been used as pH microsensor and an instrumentation amplifier as the read-out circuit. The ISFET structure is conformed by the channel length and ratio of MOS transistor, gate extended and the selective membrane, for which silicon nitride (Si₃N₄) is employed as an ion selective element. The complete design includes shielding around the pH microsensor and the readout circuit to avoid leakage of current to the substrate. The readout circuit is composed by three operational amplifiers and resistances that form the instrumentation amplifier, with a ±2.5 V bias has a 50 dB gain, power supply rejection ratio (PSSR) of 120 dB and common mode rejection ratio (CMRR) of 127 dB. The complete system is integrated in a 1.12 mm² silicon area; it presents a 59 mV/pH linearity, within a concentration range of 2 to 12 of pH level, making it a good alternative for biological or medical applications.