Study of the electroless deposition of Ni for betavoltaic battery using PN junction without seed layer

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Publisher: Hindawi Limited
Document Type: Article
Length: 2,830 words
Lexile Measure: 1380L

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The method and conditions of Ni plating were optimized to maximize the output of a betavoltaic battery using radioactive [sup.63]Ni. The difference of the short circuit currents between the pre- and postdeposition of [sup.63]Ni on the PN junction was 90 nA at the I-V characteristics. It is suspected that the beta rays emitted from [sup.63]Ni did not deeply penetrate into the PN junction due to a Ni seed layer with a thickness of 500 [Angstrom]. To increase the penetration of the beta rays, electroless Ni plating was carried out on the PN junction without a seed layer. To establish the electroless coating conditions for [sup.63]Ni, nonradioactive Ni was deposited onto a Si wafer without flaws on the surface. This process can be applied for electroless Ni plating on a PN junction semiconductor using radioactive [sup.63]Ni in further studies.

1. Introduction

A betavoltaic battery that converts the decay energy of beta-([beta]-) emitting radioisotopes into electricity is characterized by specialized properties such as a long service life and being free of maintenance [1]. The origin of nuclear batteries using beta-particle was the pacemaker related to pacing industry in 1973. These devices offered young patients the possibility of having a single pacemaker implant that could last their whole life. The [beta]-cell for pacemaker had promethium ([sup.147]Pm) sandwiched between semiconductor wafers. The impact of the [beta]-particles on PN junction causes a forward bias in the semiconductor similar to the behavior of photovoltaic cell. The [beta]-cell had an open circuit voltage of 4.7 V and a short circuit current of 115 [micro]A. However, it has a half-life of 2.6 years, at most. So, nuclear pacemakers were displaced by devices powered by lithium cells in mid-1980, due to longevity of lithium-powered batteries with approximately 10 years. The important factor affecting the performance of a betavoltaic battery is a radioisotope used as a power source. [sup.63]Ni is pure beta-emitter with a low energy spectrum of [E.sub.avg] = 17.4 keV and significantly long half-life of 100.1 years and thus is widely used as the power source of betavoltaic batteries. Tritium ([sup.3]H) has shorter half-life (12.3 years) than those of 63 Ni. However, this isotope has enough longevity, the same as lithiumpowered batteries. The beta spectrum of [sup.63]Ni is below the radiation damage threshold (approximately 200 keV for Si) of semiconductors such as Si and SiC. Also, [sup.63]Ni is easier to handle than other beta-particles such as [sup.3]H, [sup.90]Sr, and [sup.147]Pm because of its low energy spectrum and solid-metal form. For this reason, it is suitable for the power source of a beta-voltaic battery to be within the nano- to microwatt range [2-4]. There are several methods for the formation of a Ni deposit onto a substrate such as electroplating, electroless plating [5, 6], and chemical vapor deposition (CVD). Among them, the electroplating process is most commonly used for Ni deposition when using [sup.63]Ni as a power source for a battery. The Ni seed layer on a semiconductor is necessary for the deposition of Ni during electroplating, but it can...

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Gale Document Number: GALE|A462298260