Ultrasonic batch mode micromachining and its application to piezoelectric sensors for fine needle aspiration biopsy.

摘要

The development of micro-electro-mechanical systems (MEMS) is constrained by the range of materials that can be processed lithographically. Bulk ceramics (including piezoceramics) are of particular interest due to unique properties for application to micromachined transducers and packages. This effort has two goals: the development of lithography-compatible batch-mode micro ultrasonic machining (microUSM) of bulk ceramics; and the demonstration of this technology by its application to piezoelectric sensors for guiding fine needle aspiration (FNA) biopsy.;The new micromachining process, LEEDUS, uses lithography, electroplating and batch micro-electro-discharge machining (muEDM) to define stainless-steel microtools, which are then used in batch muUSM of ceramic substrates. This die-scale pattern transfer provides high throughput and resolution. A related process (SEDUS) uses serial muEDM without lithography for rapid prototyping of simple patterns. A computer-controlled muUSM apparatus with force feedback is developed as part of this effort. Die-scale patterns with 25mum feature sizes can be transferred onto Macor(TM) ceramics at a machining rate of >18 mum/min. Other process characteristics are also described. Spiral in-plane actuators are machined from bulk lead zirconate titanate (PZT) for demonstration purposes.;The process is applied to piezoelectric sensors integrated on biopsy needles to aid in real-time tissue differentiation during FNA biopsy, which is challenging because of the precision required to obtain samples from small target tissue volumes. The 200microm-diameter and 50microm-thick sensors are batch-fabricated from bulk PZT and located on a steel diaphragm formed at the needle tip by muEDM. Tissue contrast detection is demonstrated, showing resonance-frequency shifts (≈13MHz) in sensor impedance when the needle is moved between tissue layers (porcine fat/muscle). In vitro characterization shows proportional relationship between the frequency shift and sample acoustic impedance, demonstrating its potential utility during FNA biopsy. For tissue depth >15mm, differential sensor configurations are designed with oscillating interface circuits, which include an analog CMOS circuit fabricated in the UM 3mum process. The circuit functionality is experimentally verified: an inverter amplifier provides a voltage gain of >390V/V; oscillating signals of ≤19.67MHz are generated with quartz crystals. For the piezoelectric sensor to be used with this interface a higher Q is necessary and various options have been defined.