First surface mirror with chromium nitride layer

#This application is related to a first-surface mirror including a layer of or including chromium nitride (CrNx). In certain example embodiments, a reflective layer of the mirror comprises chromium nitride, and is nitrided to an extent so as to reduce undesirable pinhole formation and/or improve adhesion. In certain example non-limiting instances, such first surface mirrors may be used in the context of a projection television (PTV) apparatus, automotive mirrors, or in any other suitable application.

#Mirrors for various uses are known in the art. For example, see U.S. Pat. Nos. 5,923,464 and 4,309,075 (all hereby incorporated herein by reference). Mirrors are also known for use in projection televisions and other suitable applications. In the projection television context, see for example U.S. Pat. Nos. 6,275,272, 5,669,681 and 5,896,236 (all hereby incorporated herein by reference).

#One type of mirror is a second or back surface mirror (most common), while another type of mirror is a first or front surface mirror (less common). Back surface mirrors typically include a glass substrate with a reflective coating on a back surface thereof (i.e., not on the front surface which is first hit by incoming light). Incoming light passes through the glass substrate before being reflected by the coating in a second surface mirror. Thus, reflected light passes through the glass substrate twice in back or second surface mirrors; once before being reflected and again after being reflected on its way to a viewer. In certain instances, passing through the glass substrate twice can create ambiguity in directional reflection and imperfect reflections may sometimes result. Mirrors such as bathroom mirrors, bedroom mirrors, and architectural mirrors are typically back or second surface mirrors so that the glass substrate can be used to protect the reflective coating provided on the rear surface thereof.

#FIG. 1 is a cross sectional view of a first surface mirror according to an example embodiment of this invention.

#FIG. 2 is a graph illustrating that pinholes in a CrNx layer decrease in number as nitrogen content increases in a CrNx layer in a mirror.

#FIG. 3 is a graph illustrating that the adhesion force of protective tape to a Cr inclusive layer in a mirror decreases as nitrogen content in the layer increases, thereby indicating that durability of an exposed CrNx layer increases as nitrogen content increases since the protective tape is less likely to pull off parts of the layer when the tape is removed.

#The instant invention relates to a mirror that may be used in the context of projection televisions (PTVs), copiers, scanners, bar code readers, overhead projectors, and/or any other suitable applications. In certain embodiments, the mirror includes a layer of or including CrNx. The CrNx layer may be used as the only or primary reflective layer of the mirror in certain example embodiments of this invention. In certain example embodiments, a front surface mirror (FSM) is provided with a layer of or including chromium nitride (CrNx). The CrNx layer may be formed by physical vapor deposition such as sputtering, or in any other suitable manner in different embodiments of this invention.

#Most in the art would not add nitrogen to a reflective layer in a mirror, because nitrogen tends to degrade reflection characteristics which are of course highly desirable in mirrors. However, surprisingly and unexpectedly, it has been found the addition of nitrogen to the chromium to form CrNx reduces pinhole formations in the resulting layer, without significantly adversely affecting the mirror's reflective properties. In certain example embodiments, the more nitrogen which is introduced into the layer, the smaller the number and/or size of pinholes in the Cr inclusive layer. In certain example embodiments, it has also been found that the addition of nitrogen to Cr may also improve durability of the mirror.

#It has also been found that the addition of nitrogen tends to reduce stress of the Cr inclusive layer thereby making it closer to zero (compared to if no nitrogen was present given a Cr layer of the same thickness). Thus, the stress in layer 3 tends to be less when nitrogen is added (resulting in a CrNx layer), so that the adhesive force of layer 3 to the glass is less likely to be overcome causing delamination. Durability is improved in this respect, and this may lead to less pinholes due to improved adhesion.