HAMAMATSU: μPMT

Hamamatsu develops a new MEMS-based photomultiplier,Micro PMT (μPMT).

PMT

Photomultiplier tube is a very sensitive detector of light.  Photocathode converts photon into electron, then multiplied in each dynode stages. High gain, low noise, high frequency response and large area collection earn PMT an place in low light detection.

Dynode is an electrode which has surface exciting secondary electron, amplifying the tiny electron, typically by a factor of million.

http://en.wikipedia.org/wiki/Photomultiplier

μPMT

μPMT is ultra-compact - has only 1/7 volume and 1/9 weight. Hamamatsu implements the PMT design onto flat surface. From the picture below, light transmits the glass to photocathode from downside. Photoelectrons corresponded to incident light are emitted and guided into multiplying dynode by focusing electrode, along the direction - B.

Each has secondary electron surfaces, formed by alkali activation after deposition of aluminum(Al) and antimony(Sb), as shown as above(like a rod) and below (side view). Deep groove prevent electron leakage into insulation substrate, which avoids the decrease in withstand voltage and realize the noise reduction.

MEMS-based process

Micro PMT does not contain any moving parts like MEMS device. "MEMS-based" means that uPMT is fabricated  through the use of semiconductor process for MEMS devices. uPMT consists of three layers that silicon layer is sandwiched between two glass layers. Dynode is etched by deep RIE process on silicon layer, and then adheres with another glass layer by anode jointing. Deep RIE makes the groove 900um deep finally.

Market

• portable instrument
• medical diagnostics
• environmental monitoring
• chemical analyzer 

Due to its extremely small size, it is expected that uPMT will contribute to compact instrument for bio, health, and chemical applications.

Conventional PMT require manual assembly, but uPMT use MEMS semiconductor process designed for mass production which decrease the price of such high sensitive sensor.