Piezoresistive Feedback Control of a MEMS Thermal Actuator

Abstract

Feedback control of MEMS devices has the potential to significantly improve device performance and reliability. One of the main obstacles to its broader use is the small number of on-chip sensing options available to MEMS designers. A method of using integrated piezoresistive sensing is proposed and demonstrated as another option. Integrated piezoresistive sensing utilizes the inherent piezoresistive property of polycrystalline silicon from which many MEMS devices are fabricated. As compliant MEMS structure's flex to perform their functions, their resistance changes. That resistance change can be used to transduce the structures' deflection into an electrical signal. The piezoresistive microdisplacement transducer (PMT) is a demonstration structure that uses integrated piezoresistive sensing to monitor the output displacement of a thermomechanical inplane microactuator (TIM). Using the PMT as a feedback sensor for closed-loop control of the TIM provided excellent tracking with no evident steady-state error, maintained the positioning resolution to ±29 nm or less, and increased the robustness of the system such that it was insensitive to significant damage.

Vibration Modes and Parameter Analysis of V‐Shaped Electrothermal Microactuators

“…e analytically calculated mode shapes are based on the combination of the calculations of the lateral and longitudinal mode shapes, as in (20) and (21). e mode shapes calculated analytically also match the FEA simulation results very well.…”

“…In contrast to the traditional line-shaped beam cases, the mode shapes of the V-shaped beam involve the coupling of the lateral and longitudinal deflections. e mode shapes can be computed as in (20) and (21) with respect to the base frame XAY in Figure 2(a). W(x) and U(x) are lateral and longitudinal deflections calculated with (18) and (19), respectively.…”

“…e U- [18,19], V- [20,21], and Z-shaped [22][23][24] beams are the most fundamental actuator types in achieving the in-plane motion. A variety of structures that have been proposed are mainly based on these three types of beams.…”

Frequency Modulation Technique for MEMS Resistive Sensing

“…Several sensing techniques for precise control of MEMS micro-actuators have been proposed, offering high sensing accuracy. For instance, in [6] piezoresistive sensor is used to measure the displacement of an actuator.…”

Analysis of Nonlinear Phenomena in a Thermal Micro-Actuator With a Built-In Thermal Position Sensor

“…Micro-heaters were used to measure the motion of a MEMS micro-scanner with resolution of less than 1 nm. Also, the positions of electrothermal actuators were precisely controlled in feedback loops by onchip sensors that work based on piezoresistivity [30] or thermal variation of electrical resistivity [31]. Compared to the capacitive schemes, thermal actuation and sensing involve lower actuation voltages, smaller footprint, and less complicated circuitry and integration mechanisms [32].…”