RF MEMS technology presents a paradigm shift in space and hand held communication system architecture because of the ultra light weight devices and systems with superior performance as compared to contemporary state of the art solid state devices. Munition control and automation, bio-medical instrumentation and system automation in general present other important applications.
CSIR-CEERI along with its strategic sector partners is engaged in RF technology development which includes design, fabrication process development, characterization and packaging. The indigenous effort has resulted in demonstration of fully packaged devices at TRL 5 and higher. An innovative bio-inspired approach based on ultra low stiffness anchoring is being developed to build actuators with electrostatic excitation less than 2.5V. As an example RF MEMS switches have been demonstrated which actuate at 2.5 volts. Stress characterization test structures e.g. Guckel ring arrays, cantilever and bridge arrays, pointers, and symmetric lancets, form an integral part of the technology and are explored along side the devices. The key technology and device features include:
- Capacitive & Ohmic Contact switches – SPST, SPDT, SP4T, Switch matrices
- Electrostatic actuation: 2.5V – 20V, Frequency Range : 8GHz – 20GHz
- Insertion loss & Isolation: 0.6dB (CS) – 1.5dB (OCS) & -25dB (OCS)– -40dB (CS)
- Life time (Cold test) : >107 cycles
- Surface and bulk micro-machining for devices and packages
- Seven to nine mask level metal electroplating and high-k dielectric based technology
Digital micro mirrors resemble the toggle switches and are used as simple ón-off’ switches to create pulse of ‘digital light’. The electrostatically actuated arrays consists of a 4×4 matrix of individual mirrors (200×200 µm2) and can be individually switched on. The array resembles the digital light processing unit by Texas Instruments but smaller in size with simpler addressing mechanism and indented for multi object spectroscopy. The key features of technology under development are:
- Surface micro machining and gold electroplating
- 3×3 – 5×5 arrays with individual mirror size of 200×200 um2
- Tilt angle of 10 and /4 surface finish
- Electrostatically Actuated (10-15V) arrays with fill factor of 80%
- Limited linear (vertical) motion along with tilt
The bimorph actuator development is the logical extension of our RF MEMS technology development initiative except the selection of materials for higher deflection. In conjunction with prevalent actuation mechanisms in use, multi-morph structures add a paradigm shift towards biomimetic transducer and actuator architecture. Development of tunable dielectric resonant filter for satellite communication applications (in collaboration with strategic sector partners) is one of the immediate goals. The other indented applications include: Micro-grippers, Micro-Valves, Micro Pumps and micro-docking stations.
The key features/specifications of the technology for tunable DRBP Filter under development are: Tuning Plate Dimensions: 1000 x 1000 µm, Actuation Type: Electro-thermal, Tuning Range (z- deflection): 250 – 500 µm, Cavity: Metallized Silicon or metal, Number of segments per actuator: 3 -5, Materials: Poly silicon, SiO2, Au, Al.
The main objectives of the nondispersive, uncooled MEMS Pyroelectric Infrared detector studies and development are the safety and energy saving in gas analyses especially in the 1-15 um wavelength regime for indoor air quality and food safety monitoring. The studies include the MEMS architecture for minimal heat loss, PZT layer for detection, IR absorbing layers and packaging. The SMR- FBAR architecture involves additional polymer (PIB) layers for the ‘mass analyzer’ to perform as gas sensor. Pyroelectric IR detector and SMR-FBAR are at advanced fabrication and characterization stage.
Micro-structured semiconductor neutron detectors (MSNDs) enhance the neutron detection efficiency and overcome the limitations of coated planar diodes. In the project proposal (DRDO Collaboration) development of MSND is envisaged. Proposed high-aspect ratio deep etching (HARDE) technique facilitates the realization of compact microstructures with increased counting efficiency. The deep microstructure within the bulk semiconductor, backfilled with neutron reactive material, raises the neutron detection efficiency by increasing the neutron absorption efficiency and the probability of registering an interaction above some lower level discriminator.
Acoustic Sensors is a device, which can monitor physical, biological, and chemical stimulus by producing an electrical signal. The miniature acoustic sensor developed so far have focused primarily on hearing aid applications and therefore, most of the researchers concentrated on acoustic detection only in a limited audio range. Moreover, the measurement of high sound pressure level is an important requirement for aerospace applications because sound pressure produced by launch vehicle and large booster rocket can cause fatigue of metal panels and structures. CSIR-CEERI has developed a MEMS-based acoustic sensor for high sound pressure level (SPL) generated during Polar Satellite Launch Vehicle (PSLV) and Geosynchronous Satellite Launch Vehicle (GSLV) launching. The developed MEMS acoustic sensor chips have been delivered to Vikram Sarabhai Space Centre (VSSC), Indian Space Research Organization (ISRO) Thiruvananthapuram for their PSLV/GSLV missions. The sensor is used for monitoring the acoustic levels generated during the launch of a satellite launch vehicle. It is the first indigenously developed MEMS technology based sensor flight-tested in an Indian Launch Vehicle and has operational heritage of 12 successive PSLV flights. The structure consists with a piezoelectric zinc oxide layer, sandwiched between two aluminum electrodes on a thin silicon diaphragm. The pressure compensation in the developed acoustic sensor is achieved by using a micro-tunnel development in the structure. The measured sensor outputs such as sensitivity, sound pressure level range and bandwidth were found to be 380 mV/Pa, 120 dB to 180 dB and 30 Hz to 8 kHz respectively. The developed acoustic sensor is a substitute of imported sensor for high SPL measurement and can also be used as a microphone. It is an emerging need of high volume consumer communication device manufactures that are looking for acoustic sensing with the unique combination of high performance and low manufacturing cost. The markets and applications for this sensor include aero-space, defense and societal impact such hearing aids and medical applications etc.