This paper presents a mixed-signal closed-loop control system for Lorentz force resonant MEMS magnetometers. The control system contributes to 1) the automatic phase control of the loop, that allows start-up and keeps self-sustained oscillation at the MEMS resonance frequency, and 2) output offset reduction due to electrostatic driving by selectively disabling it. The proposed solution proof-of-concept has been tested with a Lorentz force-based MEMS magnetometer. The readout electronic circuitry has been implemented on a printed circuit board with off-the-shelf components. Digital control has been implemented in an FPGA coded with VHDL. When biased with 1 V and a driving current of 300 µA rms , the device shows 9.75 pA/µT sensitivity and total sensor white noise of 550 nT/ √ Hz. Offset when electrostatic driving is disabled is 793 µT, which means a 40.1% reduction compared when electrostatic driving is enabled. Moreover, removing electrostatic driving does not worsen bias instability, which is lower than 125 nT in both driving cases.

No abstract

Lorentz-force Microelectromechanical Systems (MEMS) magnetometers have been proposed as a replacement for magnetometers currently used in consumer electronics market. Being MEMS devices, they can be manufactured in the same die as accelerometers and gyroscopes, greatly reducing current solutions volume and costs. However, they still present low sensitivities and large offsets that hinder their performance. In this article, a 2-axis out-of-plane, lateral field sensing, CMOS-MEMS magnetometer designed using the Back-End-Of-Line (BEOL) metal and oxide layers of a standard CMOS (Complementary Metal–Oxide–Semiconductor) process is proposed. As a result, its integration in the same die area, side-by-side, not only with other MEMS devices, but with the readout electronics is possible. A shielding structure is proposed that cancels out the offset frequently reported in this kind of sensors. Full-wafer device characterization has been performed, which provides valuable information on device yield and performance. The proposed device has a minimum yield of 85.7% with a good uniformity of the resonance frequency fr¯=56.8 kHz, σfr=5.1 kHz and quality factor Q¯=7.3, σQ=1.6 at ambient pressure. Device sensitivity to magnetic field is 37.6fA·μT−1 at P=1130 Pa when driven with I=1mApp.

A first reported complementary metal-oxide semiconductor (CMOS)-integrated acceleration sensor obtained through isotropic inter-metal dielectric (IMD) etching of a back-end-of-line (BEOL) integrated circuit interconnection stack, without any additional substrate etching steps, is presented. The mechanical device composed of a CMOSprocess 8 μm-thick metal-via-metal stack of 135 μm diameter and suspended 2.5 μm over a bottom fixed electrode, has a resonance frequency of 20 kHz, a sensing capacitance of 50 fF with sensitivity 14 aF/G and it is integrated on the same substrate with a simple lownoise amplifier reaching 25 mG of RMS noise measured from 0.25 to 100 Hz bandwidth.Introduction: The micro electro mechanical systems (MEMS) inertial sensors market has experienced rapid growth because of the popularisation of consumer electronic devices such as smartphones, GPS, video game consoles and so on where the total device price and size are the critical factors [1]. Most of the currently available sensors are either multi-chip modules or fully integrated devices using a custom MEMS process. In both cases the necessity of a separate MEMS process is a bottleneck for price and size reduction trends.A possible way to address this challenge is a full integration of multiple sensors with CMOS read-out electronics using CMOS micromachining and standard back-end-of-line (BEOL) metal layers as the structural material. Existing solutions are based on reactive ion etching of the BEOL stack followed by substrate etching [2] and they do not provide sensor integration on top of the electronics. Isotropic (wet or dry) etching of the inter-metal dielectric (IMD) layers [3,4] has been applied mainly to develop relatively simple RF-MEMS devices [5,6]. Its application to inertial MEMS, where a possibly big suspended mass is needed, required additional substrate etching as well [7].Nevertheless, the presence of thick metal layers in RF-oriented CMOS and BiCMOS technologies opens a possibility of using simple isotropic IMD etching to develop monolithically integrated inertial sensors. Such sensors could become new IP cores ready to integrate in more complex SoCs and if a sufficient number of metal layers is available, a sensor integration on top of the electronics could provide a next major breakthrough for device cost and size reduction.In this Letter we present a z-axis CMOS-integrated acceleration sensor obtained using isotropic IMD etching of the BEOL interconnection stack performed without any additional substrate etching steps.