New Type of RF Switches for Signal Frequencies of up to 75 GHz Steffen Kurth Fraunhofer ENAS, Chemnitz, Germany Page 1
Contents Introduction and motivation RF MEMS technology Design and simulation Test and analysis Summary Page 2
Applications Telecommunication systems Satellites and ground stations Radar systems Automated (RF) Test Equipment CATV-and L-Band Switch modules (950 2150 MHz) Phased Array Antennas Multi-Switch-Matrix for vector network analyzer Multi-beam-antenna Source: Yole report - Sensors and Technologies for IoT Page 3 2014
RF-MEMS: Market development, switches RF-MEMS-Switches market grows by approximately 3 times from 2014 to 2019 Main target applications: telecommunication and defense Source: Yole development, Status of the MEMS industry 2015, MB67B detail from System+ consulting report: InvenSense MP67B, (2015) Page 4
Miniaturized RF Switches Products on the market 36 GHz, IL 0,5 db, IS 18 db 40-90V, 5 µs 20 GHz, IL 0.4 db, IS 30 db 24-30V, 100 µs Protron Mikrotechnik, Preliminary data sheet, Nov: 2014 http://www.radantmems.com/radantmems/s witchperformance.html, 8.6.2015 7 GHz, IL 3 db, IS 30 db 5V 33mA, 100 µs 10 GHz, IL 1 db, IS 30 db 34V, 100 µs White Pape 2SMES01 MEMS RF Switch 2013 Due to low customer demand, the Micro Device division at Omron has decided to discontinue its RF MEMS Switch product line, 2SMES-01 Page 5
Miniaturized RF Switches Research and development 75 GHz, IL 1 db, IS 20 db 5V, 15 µs 50 GHz, IL? db, IS? db 30V,? µs 2 GHz, IL 0.18 db, IS 52 db 10-20V, 5 µs Technology demonstration 40 GHz, IL 1 db, IS 20 db 30V,? µs Page 6
Sticking Charging Issue is reliability General failure risks of MEMS Switches Contact wear Large areas of electrodes or switch capacitance come into intimate physical contact (low roughness) and there is too low force to separate the contacts. Welting of α-spot, A- fritting. Dielectric materials in between electrodes accumulate surface charges or charges are trapped in the material from fabrication (e.g. anodic bonding) or from operation. Contacts physically destroyed/ deformed because of plastic deformation of too weak or too thin contact material, inclusions of dielectric residuals into the metal after mechanically breaking the insulating flayers. Contamination Organic residuals from fabrication/ packaging, water, oxide or hydrocarbons crack products on contact surface lead to high contact resistance when the contact force is not sufficiently high. Hermeticity Overload ESD Un-sufficient hermeticity leads to increased switch time (gas damping) and to risk of contact contamination. Break trough of open contact leads to physical damage of the comparably extreme small sized contact tips. Current overload results in melting of contact material, welding and generation of alloy (e.g. AuSi) witch high specific resistance. Driving electrodes and contact may be damaged by electrostatic discharge during fabrication (anodic bonding) or while handling. Page 7
Contacts of MEMS switches Contaminated cavity walls Source of further hydrocarbons Asperity with inclusion of broken isolation layer material Increased resitance Contact noise Increased nonlinearity Asperity with isolation Organic contaminants (impurity in contact metal, external source, storage at atmosphere, friction polymerization) Tunneling Electric break trough Asperity with effective conductivity Softening due to heating Creep Melting and welding Page 8
Targets of RF MEMS-Switch development Potentially high reliability of switch devices by novel technology and suitable design. 1. High force when closing and when closed, achieve stable and low contact resistance. 2. High force for separation, prevent sticking. 3. Wafer level vacuum encapsulation, and contact material deposition in on of the last fabrication steps, lowest possible contamination. 4. No dielectric material between movable and fixed structures, no charging of actuators. Page 9
MEMS Technology for RF Applications Air gap Insulated Micromachining (AIM) Process Highly resistive Si-wafers, no SOI-wafer necessary 50 µm deep movable structure, large electrode area Contact metal sputtering in contact area trough shadow mask Page 10
Cost-efficient packaging (0 level) by wafer bonding in vacuum or in inert gas Cross section of structures Photograph of a single chip Page 11
Chip layout and special features Port 1 Driving electrodes Port 2 400 µm Contacts Gap reduction mechanism and restoring springs 4 µm 4 µm Electrode gap reduction by electrostatic attraction and micro welding Page 12
MEMS Model ROM model with ABM blocks Node 1 k r m e c r k c Electrostatic force Node 2 m r Contact force F c Lennard-Jones force Finite Element Analysis of restoring spring Page 13
Simulation of force and motion Node 1 k r m e c r Dynamic force enhancement Static force enhancement k c Dynamic force enhancement Node 2 m r Contact force F c Page 14
Analysis and optimization by FDTD, 75 GHz type E-field distribution @ 50 GHz in 150 µm depth Off-state: With shield Without shield On-state: With shield Without shield Page 15
Measurements 75 GHz type Isolation, insertion loss and reflected power Page 16
RF power handling and compression point Experimental set-up Page 17
Comparison to semiconductor switches ENAS SPST 3-5 Volt 5 na 25 nw 10 µs 45 db 20 db 0.3 db (1 db) 5 W >65 dbm Source: Intellisense Page 18
Technical summary The issues are solved! General: Electrostatic driving Series and shunt switch available 3 mm x 1,5 mm x 0,5 mm flip-chip-device 4 GHz version and 75 GHz version available Benefits: Very low actuation voltage (<5 V) and short switch on time (<10 µs) Lossless actuation High contact force (>100 µn) and improved reliability of contact resistance Applications: Adaptive Antenna to improve communication quality in fast changing environment Reconfiguration of radio modules for different standards Multiplexing switch arrays for automated test equipment RF- und Contact area Insulation and insertion loss Driving electrodes Technology Readiness Level: 5 Page 19
Cooperation Fraunhofer develops new devices and technologies for transferring to industry. Fraunhofer is not a device manufacturer but provides prototypes to bridge the time between lab samples state and established volume production state. Cooperation model: 1. First samples and prototypes, Multi Client Wafers 2. Technology transfer to clients 3. Assistance in ramping up the fabrication 4. Licensing of background IP Thank you for your interest! Page 20