Sensors, Actuators & Microsystems

The Sensors, Actuators, & Microsystems team focuses on developing novel transducers at the heart of many electronic systems today, bridging the electronic and the real world. Semiconductor microfabrication techniques are leveraged for engineering high performance, microscale devices that can be batch fabricated at low-cost. Some of the key themes in the group are: acoustic sensors, piezoelectrics, as well as gas and chemical sensors.

Chemical Sensor

Mid-infrared technology platform
Photonic MEMS component design for both active and passive devices covering mid-infrared range for applications such as sensing and imaging.

Self-referenced Relative Humidity Sensor

		Schematic of the integrated photonic relative humidity sensor based on a photonic ring resonator. The resonator above in the sensor acts as a “chilled mirror” and “thermistor” simultaneously. In particular, the micro-resonator is used to 1) probe the temperature change in the environment via thermo-optic effect induced resonant wavelengths shift; 2) detect water condensation on the chip due to shift in group index.
IME has developed a miniature photonic relative humidity sensor, which has a high accuracy comparable to commercially available chilled mirror hygrometer but yet at a much smaller footprint and cost. In addition, through “in-situ” temperature sensing mechanism, IME’s sensor eliminates intrinsic temperature errors commonly observed in chilled mirror hygrometers, which are often due to the temperature gradients between the mirror and platinum resistance thermometer (PRT).

Acoustic MEMS

Aluminum nitride technology platform
Aluminum nitride (AlN) is a piezoelectric material that can readily be deposited as thin-films on the wafer level. These piezoelectric properties are valuable for MEMS devices as they convert mechanical energy into electrical energy and vice versa. This enables mechanical stresses to directly generate electrical signals (for sensors) or mechanical movements to be achieved with electrical stimuli (for actuators). IME has developed numerous wafer fabrication technology platforms based on AlN for MEMS devices, such as for resonators, energy harvesters, ultrasonic transducers, and other sensors.

Piezoelectric Micromachined Ultrasound
Ultrasound is used in distance ranging, medical imaging, fingerprint imaging, and non-destructive testing. IME has been developing piezoelectric micromachined ultrasonic transducers (pMUTs), which are miniature ultrasonic transducers fabricated using MEMS wafer processing technology. These transducers are much slimmer compared to traditional ultrasound transducers, and can be used in space-constrained locations or for wearables. The transducers can also be directly fabricated on integrated circuits, enabling high quality, high complexity ultrasound imaging.

Hydrophone
Hydrophones are underwater microphones. They are able to detect underwater sounds for applications such as pipeline monitoring, underwater communication, fish/ocean mammal research, and ocean resource exploration. IME has developed a miniaturized hydrophone sensor using piezoelectric MEMS technologies. These MEMS hydrophones have significant advantages such as low cost, small size, high signal-to-noise ratio, and low power consumption.

MEMS for RF & Computation

RF MEMS Resonators and Filters

IME is capable for design, simulation, modeling, and prototyping of RF MEMS devices with excellent performances. Our AlN based Laterally Coupled Alternating Thickness (LCAT)-mode resonator achieves ultra-high coupling coefficient (>6 %). Our FBAR-based Ladder type filter exhibits low insertion loss and wide band with the center frequency ranging from 2 GHz to 4 GHz.
Wafer level device characterization and analysis are well established, with high power (up to 38 dBm) and wide temperature range from -60 to 300 °C.

RF MEms Integration Platform

In 5G era, the RF spectrum gets increasingly crowded. The front-end bandpass filters are becoming the most important element in wireless communication devices.
IME has established 8-inch AlN and ScAlN integration platform with complete module technologies including lithography, PVD, CVD, etching, passivation, and thin film capsulation processes. This platform can host various types of the devices, such as FBAR, Lamb wave resonators, LCAT mode resonators, and so on. On top of it, monolithic integration of RF MEMS devices on COMS was also developed.
Extra efforts are invested to study the AlN and ScAlN films. On our advanced manufacturing grade 8-inch PVD and dry-etching platform, high quality AlN and ScAlN film deposition and patterning are well established. Currently we are working on the ScAlN films with Sc concentration up to 20%, and 30 % ScAlN development will start in near future.

Optical Sensors

RGB Colour Display

(a) Photograph of the fabricated 12-inch wafer. (b) Close view of the color display with colored logo “IME” within one die on the wafer. (c)-(e) scanning electron micrographs of a-Si nanopillar arrays for the three letters “I”, “M” and “E”, respectively

A color display metasurface on a 12-inch silicon wafer with critical dimension (CD) below 100 nm by complementary metal-oxide semiconductor (CMOS) compatible technology is demonstrated for the first time. The 193 nm ArF deep UV immersion lithography is used to pattern the metasurface, which as compared to electron beam lithography (EBL), greatly improves the efficiency while keeping a high resolution. The demonstrated metasurface successfully generates different resonances at the red, green, blue (RGB) wavelengths, making the RGB display possible.

Metalens

An amorphous silicon (a-Si) metalens on a 12-inch glass wafer via the 193 nm ArF deep UV immersion lithography, with critical dimension (CD) as small as 100 nm. The layer transfer technology is developed to solve the glass wafer handling issue in complementary metal-oxide-semiconductor (CMOS) fabrication line. The measured numerical aperture (NA) is 0.494 with a beam spot size of 1.26 μm.

POLARIZATION BANDPASS FILTER

The high-performance and mass-producible polarization controller based on Si metasurface is in high demand for the next-generation SWIR imaging system. The first demonstration of all-Si metasurface based polarizing bandpass filters (PBFs) on 12-inch wafers. The PBF achieves a polarization extinction ratio of above 10 dB in power within the passbands. A device yield of 82% is achieved.

Dot Projector

An ultra-thin and large-area pixelated metasurface beam deflector with a footprint of 2500 × 2500 μm, formed by nanopillars with diameters from 221 to 396 nm, is demonstrated on a 12-inch glass wafer. The 21 × 21 array of deflectors is designed to bend the input light in different directions and to generate 441 random points. This pixelated metasurface beam deflector can generate random points simultaneously and has potential to make beam steering by switching each pixel of the beam deflector, which can be applied on motion detection, facial recognition, and light detection and ranging.

Emerging Memories

DIGITAL MEMORY TOWARD STORAGE CLASS MEMORY

As the CMOS technology advances with Moore’s Law, the discrepancy of memory access time also grows between working memory (DRAM) and SSD storage (NAND FLASH). Emerging memory devices such as resistive RAM (ReRAM) has been regarded as an attractive candidate to close such access time gap in near future with additional memory capacity bonus over DRAM.
IME is capable of both 8-inch and 12-inch platform for sub-100nm ReRAM integration with CMOS technology down to 40nm. We are aiming for high memory bandwidth and high performance memory for storage class memory (SCM) applications. We have demonstrated the 64kb ReRAM array integrated with 180nm CMOS back-end-of-line (BEOL) technology.

ANALOG MEMORY FOR IN-MEMORY COMPUTING

Conventional computer with separated processor and memory units is suffering from a crucial bottleneck for efficient data movement. On the other hand, innovative computing paradigms such as in-memory computing are intensively studied to further enhance computing energy and time efficiencies toward next milestone. Besides, memory elements with capability of multi-level states per cell with the cross-point array integration forms a promising hybrid memory-computation unit for in-memory computing paradigm. Moreover, analog behavior in ReRAM is also one of the few memory technologies to present synaptic-like programming response as in biological observations, which is an essential building block for neuromorphic computing hardware.
IME dedicates to the development of analog memories such as ReRAM and FeRAM in order to achieve high performance and high energy efficiency in-memory computing system. We have shown case the Al2O3/Ta2O5 based bilayer ReRAM with analog switching characteristics for synaptic applications.