Features

• Ion implanted contacts
• SiO₂ passivated
• Low leakage current
• Low noise
• Thin window
• Cleanable
• Bakeable to 100 °C

Description

CANBERRA 's Passivated Implanted Planar Silicon (PIPS) Detector is a product of modern semiconductor technology. In most applications, this detector replaces silicon surface barrier (SSB) detectors and diffused junction (DJ) detectors, both of which are still made the same way they were made in 1960. The PIPS detector has a number of advantages over SDB and DJ types:

1. All junction edges are buried - no epoxy edge sealant is needed or used.
2. Contacts are ion-implanted to form precise, thin, abrupt junctions for good alpha resolution.
3. Entrance window is stable and rugged - it can be cleaned readily and reliably.
4. Leakage current is typically 1/8 to 1/100 of that of SSB and DJ detectors.
5. Dead layer (window) thickness is less than that of comparable SDB or DJ detectors.
6. Standard detectors are bakeable to 100 °C - higher for special models.

The PIPS Detector is fabricated by the planar process using photolithographic techniques for defining device geometries. Proprietary techniques are used to provide precise control of the oxide passivation, and ion implantation is used to form the accurately controlled junctions necessary for low reverse leakage currents and thin entrance windows. The photolithographic technique lends itself to virtually any geometry which fits onto a diameter of 140 mm.

Resistivity of the uniform ion-implanted contacts can be controlled accurately to produce position-sensitive detectors with extremely thin entrance windows (<50 nm).

Low reverse current translates into low noise contribution. Shown by the newly introduced X-PIPS™ detector, an excellent room-temperature X-Ray detector.

Unlike SSB detectors which have raw junction edges that are epoxy sealed to achieve some measure of stability, the PIPS detector junctions are all buried within the silicon wafer. There are three major advantages to this innovation: 1) The device stability is not dependent upon an epoxy sealant; 2) There is little risk of microplasma breakdown which can afflict SSB detectors and 3) Leakage current is a small fraction of that of SSB or DJ detectors.

The face contact (entrance window) of the PIPS detector is ion-implanted. CANBERA has developed proprietary techniques for minimizing window thickness while retaining the ruggedness, reliability and stability inherent in this type of contact. The PIPS detector has a window that is substantially thinner than conventional SSBs and far thinner than any detector approaching it in ruggedness. A comparison is shown below:

This thin window not only improves typical resolution as normally measured but it exhibits an even greater improvement at close detector-source spacing which is necessary to achieve the high efficiency required for low-level alpha spectroscopy. The reason for this is very simple - at close detector-source spacing, peak broadening occurs because many alphas enter the detector at an acute angle - with a resultant variation in energy loss (or straggling) in the entrance window. With thinner windows, less straggling occurs.

Since the PIPS detector does not rely on delicate evaporated metallic contacts as do SSB detectors, but rather a passivated, implanted surface, it can be touched by hand and cleaned readily with a cotton ball dampened with isopropyl alcohol. This facility makes it possible to exploit applications heretofore reserved for diffused junction detectors which cannot compete with the PIPS in leakage current, resolution or window thickness.