Margarita Narducci

CMOS MEMS capacitive absolute pressure sensor

This paper presents the design, fabrication and characterization of a capacitive pressure sensor using a commercial 0.18??m CMOS (complementary metal?oxide?semiconductor) process and postprocess. The pressure sensor is capacitive and the structure is formed by an Al top electrode enclosed in a suspended SiO2?membrane, which acts as a movable electrode against a bottom or stationary Al electrode fixed on the SiO2?substrate. Both the movable and fixed electrodes form a variable parallel plate capacitor, whose capacitance varies with the applied pressure on the surface. In order to release the membranes the CMOS layers need to be applied postprocess and this mainly consists of four steps: (1) deposition and patterning of PECVD (plasma-enhanced chemical vapor deposition) oxide to protect CMOS pads and to open the pressure sensor top surface, (2) etching of the sacrificial layer to release the suspended membrane, (3) deposition of PECVD oxide to seal the etching holes and creating vacuum inside the gap, and finally (4) etching of the passivation oxide to open the pads and allow electrical connections. This sensor design and fabrication is suitable to obey the design rules of a CMOS foundry and since it only uses low-temperature processes, it allows monolithic integration with other types of CMOS compatible sensors and IC (integrated circuit) interface on a single chip. Experimental results showed that the pressure sensor has a highly linear sensitivity of 0.14?fF?kPa?1?in the pressure range of 0?300?kPa.

A Monolithically Integrated Pressure/Oxygen/Temperature Sensing SoC for Multimodality Intracranial Neuromonitoring

A fully integrated SoC for multimodality intracranial neuromonitoring is presented in this paper. Three sensors including a capacitive MEMS pressure sensor, an electrochemical oxygen sensor and a solid-state temperature sensor are integrated together in a single chip with their respective interface circuits. Chopper stabilization and dynamic element matching techniques are applied in sensor interface circuits to reduce circuit noise and offset. On-chip calibration is implemented for each sensor to compensate process variations. Measured sensitivity of the pressure, oxygen, and temperature sensors are 18.6 aF/mmHg, 194 pA/mmHg, and 2 mV/°C, respectively. Implemented in 0.18 m CMOS, the SoC occupies an area of 1.4 mm × 4 mm and consumes 166 μW DC power. A prototype catheter for intracranial pressure (ICP) monitoring has been implemented and the performance has been verified with ex vivo experiment.

A pressure/oxygen/temperature sensing SoC for multimodality intracranial neuromonitoring

A fully integrated SoC for multimodality intracranial neuromonitoring is presented. This SoC includes a capacitive MEMS pressure sensor, an electrochemical oxygen sensor, a solid-state temperature sensor and sensor interface circuits in a single chip. Chopper stabilization and dynamic element matching techniques are applied in sensor interface circuits to reduce circuit noise and offset. On-chip calibration is implemented for each sensor to compensate process variations. Measured accuracies of the pressure, oxygen, and temperature sensors are ±1 mmHg, ±1 mmHg, and ±0.2 oC, respectively. Implemented in 0.18-μm CMOS, the SoC occupies an area of 1.4 mm × 4mm and consumes 188-μW DC power.

CMOS-MEMS capacitive sensors for intra-cranial pressure monitoring: Sensor fabrication & system design

Low-frequency variation of intracranial pressure (ICP) is a key indicator determining the successful outcome of a patient, subjected to traumatic brain injury (TBI). Post-trauma ICP increase can lead to fatal secondary injuries and hence continuous ICP monitoring would be an essential modality required in a neuro-monitoring system. This paper discusses the system design considerations of an integrated CMOS-MEMS sensor system for monitoring ICP in patients subjected to TBI. Design and fabrication steps of the on-chip CMOS-MEMS sensor are presented first. Interface circuit design challenges introduced by the low, not-well-controlled MEMS sensitivity and large offset due to the fabrication tolerance are discussed next. A review and comparison of the reported capacitive sensors and their interface circuits follows. The paper concludes discussing the biocompatible packaging of the system for in-vivo testing.

Dual MEMS Resonator Structure for Temperature Sensor Applications

This paper reports an acoustic microelectromechanical system (MEMS) resonator structure that features dual-resonant response at 180 and 500 MHz. The MEMS structure uses aluminum nitride as acoustic layer and electrodes with dual design that provide dual-resonance behavior. Each resonant mode operates at the first symmetrical Lamb-wave mode (S0). Due to the large frequency separation between modes, device exhibits differentiated temperature coefficient of frequency) for each mode, which makes this structure suitable for thermometric beat frequency sensing. Reported devices are thus capable to multiply the 20-ppm/°C thermal sensitivity of the individual sensors by one order of magnitude, up to −334 ppm/°C for the thermometric beat frequency sensor.

RF-Designed High-Power Lamb-Wave Aluminum–Nitride Resonators

We report Lamb acoustic wave resonators that are suitable for RF applications and that exhibit high power handling at high frequencies above 1 GHz. Resonators use aluminum-nitride as acoustic layer and are fabricated in the Institute of Microelectronics (IME) Agency for Science, Technology and Research (A*STAR)s in-house RF microelectromechanical system silicon-on-insulator platform. We focus the study on devices operating at their first symmetric Lamb-wave mode (S0) at 900 MHz and 1.5 GHz, although demonstrate 400 MHz and 1.2 GHz as well. All devices are realized in the same multi-frequency platform. Assessment of devices covers gain compression point (P1dB), third-order intermodulation intercept point (IIP3), thermal management, impedance matching, and quality factor. Devices exhibit P1dB above +30 dBm, and IIP3 higher than +50 dBm with low insertion losses less than 3 dB and 50- Ω impedance matching.

Integration of RF MEMS resonators and phononic crystals for high frequency applications with frequency-selective heat management and efficient power handling

We report a radio frequency micro electromechanical system (RFMEMS) device integrated with phononic crystals (PnC) that provide a Lamb-wave resonator with frequency-selective heat management, power handling capability, and more efficient electromechanical coupling at ultra high frequency (UHF) and low microwave bands. The integrated device is fabricated in a silicon-on-insulator (SOI) aluminum nitride (AlN) platform and boosts thermal performance by 40%, power handling by 3 dB, and coupling coefficient by three times. Design approach is scalable to higher frequencies.

Cavity-enhanced sacrificial layer micromachining for faster release of thin film encapsulated MEMS

This paper reports a method for fast-release and safe-sealing of thin film encapsulation (TFE) for packaging of piezoelectric MEMS devices fabricated on cavity-SOI wafers. For fast releasing of the TFE, MEMS device trenches and the cavity below them were utilized and this combination acted as etch channels. Etchant can attack the sacrificial layer from the bottom of the MEMS device as well as side-located channels. A side-located etch channel scheme was chosen to ensure safe-sealing without mass-loading. 120 µm  ×  120 µm sized encapsulation on top of the MEMS device with eight isolation trenches connected to the cavity was released in 25 min. This is twice as fast as the TFE fabricated on bulk wafer using a similar encapsulation scheme. This reduction in release time is a consequence of a prefabricated cavity underneath the device which allows the etchant to attack the sacrificial layer at multiple locations as etchant can pass from one isolation trench to another.

Biocompatible packaging development for an intracranial microsystem

Traumatic brain injury (TBI) can be worsen by the secondary brain injury which will the major prognostic factor for the patient condition. The major parameters for monitoring the TBI are the intracranial pressure, partial brain oxygen level and the brain temperature. This leads to the development of an integrated intracranial microsystem which effectively monitored the condition of the TBI patient. This paper will present the biocompatible packaging and its in-vitro result for the microsytem.