New generation of ultrasound transducers manufactured by epoxy gel-casting

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New generation of ultrasound transducers manufactured by epoxy gel-casting Daniel Sanmartin, Carl Meggs and Tim Button Applied Functional Materials Ltd.

1 New generation of ultrasound transducers manufactured by epoxy gel-casting Daniel Sanmartin, Carl Meggs and Tim Button Applied Functional Materials Ltd. Technologies for high precission microreplication of ceramic materials 30 May 2016, EuSPEN micromanufacturing workshop, Nottingham 1FaBiMed EuSPEN micromanufacturing workshop 30 / 05 /

2 INDEX Introduction to high frequency ultrasound transducers Piezoelectric composites fabrication methods Fabimed aims and progress Ultrasound transducer demonstrators Summary Acknowledgements 2FaBiMed EuSPEN micromanufacturing workshop 30 / 05 /

AFM Products Breakthrough in High Frequency

Single Element transducers fully developed.

Strong IP (Patents, know-how, equipment).

technology. Unique patented device designs.

3 AFM Products Breakthrough in High Frequency Ultrasound Imaging. Single Element transducers fully developed. Arrays technology demonstrated up to 100MHz. Strong IP (Patents, know-how, equipment). World leading and proven processing technology. Unique patented device designs. Increased imaging resolution. AFM single element transducers AFM Packaged Prototype Array 3

4 Ultrasound Technology Safe, inexpensive, real time - >20% of all clinical scans. Widely used in Fetal imaging, Cardiac imaging, Blood flow measurement, Intra-operative guidance. Utilises machined piezoelectric ceramic element Minimum image feature size 150um at 10MHz Current commercial limit ~15MHz. For imaging: Mechanical scanning (standard for frequencies <15MHz) Single element transducer Electronic scanning Array transducer 4

5 The Ultrasound Market Global Market with multiple industry sector applications in Medical, NDT and SONAR. AFM target market: Dermatological and intravascular medical sectors. High Frequency Devices (>20 MHz). 5

1-3 piezocomposites fabrication: Dice and Fill PZT pillar Epoxy matrix Dimension requirements Frequency 20 MHz 40 MHz Pillar width 24 μm 14 μm Kerf 20 μm 8 μm Thickness 80 μm 40 μm 1-3 piezocomposite

6 1-3 piezocomposites fabrication: Dice and Fill PZT pillar Epoxy matrix Dimension requirements Frequency 20 MHz 40 MHz Pillar width 24 μm 14 μm Kerf 20 μm 8 μm Thickness 80 μm 40 μm 1-3 piezocomposite Piezocomposites made almost exclusively by the dice-and-fill technique for f<20mhz Impossible to fabricate high frequency arrays by dice and fill because of the ultrafine feature size required. Conventional dice-and-fill technique 6

7 1-3 Composite Fabrication: Viscous plastic processing (VPP) Ceramic powder, polymers and solvents w 1 Ceramic paste w 2 High Shear Mixing Electrodes Calendering Moulding Epoxy resin Polymer Mould Lapping, Poling & Electroding Vacuum Casting Demoulding & Sintering Green Ceramic 7

8 1-3 Composite Fabrication: Viscous plastic processing (VPP) a) b) c) d) Sintered ceramic pillar structures manufactured by VPP.: a, b) Hexagonal pillars in an hexagonal arrangement; c,d) Cylindrical pillars on a cylindrical arrangement 8

9 1-3 Piezocomposite Fabrication: Gel casting CERAMIC POWDER ORGANIC MONOMER SOLVENT DISPERSENT Capability of producing complex parts Homogeneous material properties MIXING SLURRY Rapid forming circle INITIATOR De-airing Low capital equipment cost. CASTING Drying Microsized mould DE-MOULDING PZT slurry De-moulding SINTERING Flow chart of gel casting process. Gel casting for 1-3 piezocomposite fabrication. 9

10 1-3 Piezocomposite Fabrication: Gel casting PDMS mould obtained from a silicon etch master mould with a randomised pattern + Gelcasting Height: 140 μm Smallest features: 2 μm Aspect ratio: up to 70 10

11 1-3 Composite Fabrication: Summary Dice and Fill Viscous Plastic processing (VPP) Gel-casting Frequency <15MHz MHz MHz Re-usable mould? Randomised patterns? Scalable? Technology dependencies N/A, direct machining process No No, sequential process No, lost mould method Limited to simple pillar shapes Yes Dicing Direct laser drilling, or Excimer laser drilling + Mask Yes Yes Yes Silicon etching and elastomer replication, or Lithography, or LIGA/ UV LIGA, or Laser drilling FaBiMed EuSPEN Micromanufacturing workshop 30/05/

12 1-3 Composite Fabrication: Technological Challenges Composite and array fabrication increasingly difficult as dimensions decrease with increasing frequency Difficult to achieve required pillar aspect ratios, which may lead to spurious modes Current lost mould method are very expensive for both gel-casting and VPP routes (Silicon etching and PDSM replication; and Excimer laser machining through a mask respectively) 12

13 Fabimed Aims: Develop Gel-casting on laser drilled elastomeric moulds manufacturing route Comparison with current VPP manufacturing route Achieve moulds re-usability and an scalable process Achieve large areas (>10mm x 10mm), for enabling scalability towards a wafer scale process. Achieve technical specifications (20-100MHz): High aspect ratio >10:1 High volume fraction >40% Pillar diameter: 15-40micron Piller height: micron Pillar kerf: 8-25micron 13

FaBiMed Progress so far: Series 1: Epoxy on PDMS moulds Series 2: PZT on PDMS moulds Series 3 (UAVR): Alumina

improve: Automated De-moulding not successful 5.3 pillar aspect ratio (Height/pillar base) is too low.

$Pillar volume fraction Achieved: Whole areas demoulded manually successfully (almost) Pillar aspect ratio$

14 FaBiMed Progress so far: Series 1: Epoxy on PDMS moulds Series 2: PZT on PDMS moulds Series 3 (UAVR): Alumina Slurry on PDMS moulds Achieved: Volume faction at pillar base ~48% Tall pillars (~180 micron) Issues to improve: Automated De-moulding not successful 5.3 pillar aspect ratio (Height/pillar base) is too low. Achieved: Tall sintered pillar structures (~170micron) Sintered PZT pillars Issues to improve: De-moulding Pillar volume fraction Achieved: Whole areas demoulded manually successfully (almost) Pillar aspect ratio look better meeting 30 Month Issues to improve: De-moulding Pillar volume fraction 14 FaBiMed Pillar height (mould filling) 14

15 FaBiMed Progress so far: Series 4: Epoxy pillars on elastomeric moulds (top), and green gel-cast material on elastomeric mould (bottom). 400um 200um Base De-moulded green ceramic pillars (~500 micron tall) 15

16 FaBiMed Progress so far: Achieved so far: Very tall pillars (~500 microns) High aspect ratios (>10:1) using laser drilled elastomeric moulds High volume fractions (~30%). Large areas (8mm x 8mm) manufactured by both VPP and gelcasting on a direct laser drilled polycarbonate mould (lost mould method) Currently working on: Gel-casting and demoulding trials currently being carried out to optimise the de-moulding of the pillar structures 16

17 Planned demonstration activities: Design of the Demonstrator: Ultrasound Transducer Demostrator for Fabimed: Single element transducer Wire (Back) Wire (Front) Tungsten Insert with wires 30 degree chamfer Tungsten loaded epoxy 17

18 Planned demonstration activities: Design of the Demonstrator: Ultrasound Transducer Demostrator for Fabimed: Single element transducer Silver paste/conductive epoxy Wire (Front) Tungsten Insert with wires 30 degree chamfer Tungsten loaded epoxy 18

19 Planned demonstration activities: Design of the Demonstrator: Ultrasound Transducer Demostrator for Fabimed: Single element transducer Silver paste/conductive epoxy Wire (Front) Tungsten Insert with wires 30 degree chamfer Tungsten loaded epoxy 19

20 Planned demonstration activities: Design of the Demonstrator: Ultrasound Transducer Demostrator for Fabimed: Single element transducer Laser machined piezoelectric composite Wire (Front) Tungsten loaded epoxy Inactive Electrode Front Electrode (1.5mm diameter) 30 degree chamfer 20

Planned demonstration activities: Design of the Demonstrator: Ultrasound Transducer Demostrator for Fabimed: Single element transducer Laser

21 Planned demonstration activities: Design of the Demonstrator: Ultrasound Transducer Demostrator for Fabimed: Single element transducer Laser machined piezoelectric composite Electrode pad (front) Tungsten loaded epoxy Inactive Electrode Front Electrode (1.5mm diameter) 30 degree chamfer 21

Planned demonstration activities: Transducer assembly:

the tips of the chamfered inserts and connections made

Transducer characterization: Impedance analysis, laser

22 Planned demonstration activities: Transducer assembly: Composites to be bonded with tungsten loaded epoxy to the tips of the chamfered inserts and connections made with silver paste. Transducer characterization: Impedance analysis, laser vibrometry, pulse-echo and imaging of phantoms. a) Intravascular version b) needle version 1.6mm 22

23 Summary Review of piezoelectric composites manufacturing (dice and fill, viscous plastic processing (VPP) and gel-casting. Fabimed aims and objectives Fabimed progress so far (tall pillars, high aspect rations, ~30% volume fractions, large areas). Upcoming ultrasound transducer demonstrator. 23

European Union Seventh Framework Programme FP7/2007-2013 under grant

24 Acknowledgement Thanks for your attention. The work leading to this results has received funding from the European Union Seventh Framework Programme FP7/ under grant agreement n Daniel Rodriguez Sanmartin Senior R&D Scientist AFM Daniel.sanmartin@afm-ltd.com 24

Passive Polymer. Figure 1 (a) and (b). Diagram of a 1-3 composite (left) and a 2-2 composite (right).

Passive Polymer. Figure 1 (a) and (b). Diagram of a 1-3 composite (left) and a 2-2 composite (right). MINIMISATION OF MECHANICAL CROSS TALK IN PERIODIC PIEZOELECTRIC COMPOSITE ARRAYS D. Robertson, G. Hayward, A. Gachagan and P. Reynolds 2 Centre for Ultrasonic Engineering, University of Strathclyde, Glasgow,