Understanding Thin Film and Thick Film Products

In the realm of electronic components, Thin Film and Thick Film products represent two distinct categories with unique characteristics. This document aims to elucidate the differences between Thin Film and Thick Film components, shedding light on their applications, advantages, and manufacturing processes.

Thin Film vs. Thick Film: A Thickness Perspective

The primary disparity between Thin Film and Thick Film products lies in the thickness of the resistive material. Thin Film components typically feature a resistive thickness of 0.1 micrometers (um) or smaller, while Thick Film components are significantly thicker, measuring in thousands of times the thickness of Thin Film.

Manufacturing Processes

1. Thin Film:

• Method: Thin Film products are most commonly created in a specialized chamber by a process called “sputtering.”  The substrate on which the film is to be deposited and a target comprised of the film material are both placed in the chamber, and a voltage applied between them.  The chamber is initially evacuated, then filled with a gas, usually argon or oxygen or some mixture of the two.  A plasma is created by ionizing the gas, charged particles of which then bombard the target and sputter off the material to be deposited.  A mask on the substrate ensures the particles are deposited in the desired pattern.
  Depending on the end product, the entire process may involve more than one material successively sputtered, either by changing targets or by using different compartments in a larger chamber.  For example, a thin-film resistor typically has an initial (often proprietary) layer to facilitate substrate adhesion, followed by the actual resistor layer (typically nichrome or tantalum nitride).  A stabilization bake in air then produces a self-passivating oxide layer that prevents future value changes.  A final step in the production process may involve laser trimming of the dimensions to achieve, for example, a precise value of resistance.
• Characteristics: This process results in precise layers of deposited materials, typically several hundred angstroms in thickness (1 Angstrom = 10-4 microns) that can be applied to a variety of substrates with varying dielectric constants and thermal conductivities , e.g., alumina, beryllia, aluminum nitride, quartz, etc.

2. Thick Film:

• Method: Thick Films are produced by screening and then firing specialized pastes onto a variety of substrates. For resistors, the paste generally consists of a binder/carrier/metal oxide combination. The binder is a glassy frit and the carrier consists of organic solvents and plasticizers. Metal oxides are typically those of ruthenium, iridium, or rhenium.
• Characteristics: The firing process leads to layers that typically range from 1 to 100 microns in thickness, and that can be applied to the same substrate varieties as thin-films. The glass-like finish is moisture protective, although a final layer of epoxy is often added for additional shielding.

Comparison of Thin-Film and Thick-Film Properties

Understanding the characteristics of Thin-Film versus Thick-Film technologies is crucial for selecting the appropriate component for a given application. Typically, thin-films are used for resistors, attenuators, single-layer capacitors, and planar spiral inductors, while thick-films are used for resistors, attenuators, and multi-layer capacitors. Below are listed some comparative properties of the two technologies for resistors.

*Resistor noise generally consists of two components, one (“Johnson noise”) that depends solely on the resistor value and temperature and is independent of frequency, and an “excess” contribution that depends on current and varies inversely as a power of frequency.

In summary, Thin-Film and Thick-Film components serve distinct purposes in electronic applications. The choice between them depends on the specific requirements of the circuit, considering factors such as accuracy, stability, frequency of operation, noise generation, and, of course, cost.